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Adaptation of dementia screening for vision-impaired older persons
Journal of Clinical Epidemiology 55 (2002) 909–915
Adaptation of dementia screening for vision-impaired older persons Administration of the Mini-Mental State Examination (MMSE) Anja Busse*, Astrid Sonntag, Jeannette Bischkopf, Herbert Matschinger, Matthias C. Angermeyer Klinik und Poliklinik für Psychiatrie der Universität Leipzig, Johannisallee 20, 04317 Leipzig, Germany Received 20 August 2000; received in revised form 13 March 2001; accepted 24 April 2002
Abstract In epidemiologic field studies on the prevalence and incidence of dementia the problems associated with the cognitive testing of visually impaired individuals are rarely discussed. In the Leipzig Longitudinal Study of the Aged (LEILA 75) a version of the Mini-Mental State Examination for the visually impaired (MMSE-blind) was employed from which all items requiring image processing had been omitted. To be able to interpret the test results and include vision-impaired individuals in the field study, the scores for the full MMSE were estimated by conducting linear transformation of the scores obtained on the MMSE-blind. The method of linear transformation is based on certain theoretical assumptions that are examined in this article. Linear transformation of scores has proved to be a valid procedure only for individuals with very high or very low cognitive performance. Thus, evaluation of the estimated full MMSE scores based on the norms for the original MMSE is not recommended. A blind version of the MMSE with age- and education-specific norms that has been validated as a screening tool for dementia is therefore presented. © 2002 Elsevier Science Inc. All rights reserved. Keywords: Dementia; MMSE; Visual impairment; Norms; Validity
1. Introduction Vision impairment, a common phenomenon in old age, leads to problems with cognitive testing and the detection of dementia in old people [1–3]. Vision-impaired individuals are often unable to respond to test items requiring image processing. Resulting missing values in cognitive tests lead to difficulties in interpreting test results. Screening instruments for detecting dementia whose items are partly vision dependent thus need to be adapted for administration to visionimpaired individuals. This raises the question as to whether such adapted tests lead to a valid diagnosis or whether they lose discriminative power in the detection of dementia [2]. The problem of vision impairment in the detection of dementia is rarely discussed in the literature. Epidemiologic studies on the prevalence and incidence of dementia hardly mention this problem. Some studies have excluded individuals with sensory impairment as ”not testable,” or have not interpreted their test results [4,5], which fails to take into account the fact that there may be a higher proportion of dementia cases in this group of individuals [6,7]. Other studies have estimated miss* Corresponding author. Tel.: 0341/97 24 530; fax: 0341/97 24 539. E-mail address: [email protected] (A. Busse).
ing responses on the basis of valid responses [5,8], thus establishing a procedure for integrating vision-impaired subjects in epidemiologic studies. However, these studies did not always investigate whether assessments of cognitive functioning based on this estimation of scores are, in fact, valid. Reischies and Geiselmann [2] reported that omitting vision-dependent MMSE items does not reduce the discriminative power of the MMSE (Mini-Mental State Examination). Neither the sensitivity nor the specificity of their version of the MMSE for the visually impaired was lower than those of the full MMSE. However, the authors of this study found that their cutoffs for the original MMSE were ”higher than in comparable epidemiological studies” and their ”values for sensitivity and specificity . . . slightly lower than those reported in the literature.” The reported reasons for these results may also have influenced the cutoffs of the MMSE version for the visually impaired. Norms for this MMSE version were presented only for different age groups, and effects of education were not analyzed. Moreover, the question as to whether the process of responding to items of the blind version is truly independent of vision impairment was not addressed. Although understanding and answering an item in the test situation may not require image processing, the ability to process images in everyday life could affect a person’s knowledge of certain facts or events. Vision-impaired people
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are, for example, unable to read newspapers or calendars, and may thus be less likely to know the date. Items that are not independent of vision in this sense should be excluded from a blind version of a screening test because they lack discriminative power in detecting dementia. In sum, recent studies have introduced two possible procedures for including vision-impaired subjects in epidemiologic studies: first, estimation of missing values on the basis of valid responses, and second, omission of all vision-dependent items from the test and establishment of norms for a reduced test version for vision-impaired people. Taking the MMSE as an example, this article aims to answer the following questions regarding these two procedures: (1) is the estimation of full MMSE scores a valid method for examining and interpreting cognitive performance with the aid of screening instruments that include vision-dependent items, such as the MMSE? (2) Are responses to the items of the blind version of the MMSE introduced by Reischies and Geiselmann (1997) [2] in fact unaffected by vision impairment? (3) Does the MMSE retain its validity when all items are omitted that require (direct and indirect) image processing to make a blind version? To date, the problem of vision impairment in the detection of dementia has remained unsolved. The aim of the following study is to contribute to the assessment and diagnosis of vision-impaired older persons in both epidemiologic studies and clinical practice.
2. Methods 2.1. Subjects The data were derived from the baseline assessment of a population-based study on the epidemiology of dementia (Leipzig Longitudinal Study of the Aged, LEILA 75) carried out from January 1997 to June 1998. A total of 1,500 community-dwelling individuals aged 75 and over and resident in the Leipzig-South district, Germany, were identified by systematic random sampling from an age-ordered list provided by the local registry office. Institutionalized individuals were included in the study on a proportional basis (n 192). The study design of the Leipzig Longitudinal Study of the Aged has been described in detail elsewhere [9]. Of the overall sample of 1,692 subjects, 242 (14.2%) declined to participate, 57 (3.4%) had died, and 15 (0.9%) were not traceable. Information on 113 (6.7%) study subjects who were shielded by their relatives was obtained solely by proxy interviews. Clinical interviews incorporating neuropsychologic assessment (including the MMSE) were conducted with 1,265 (74.8%) participants. These 1,265 study subjects did not differ significantly from the remainder of the sample in regard to age (U 263,553, P .455), gender (2 0.391, df 1, P .532) or marital status (2 5.027, df 3, P .170). The results of the cognitive tests of 22 participants with mental retardation or other psychiatric disorders were excluded. A further 107 subjects were excluded from the analysis for other reasons (i.e., because too little was known about the quality
of their vision or because an abridged version of the MMSE version had been administered owing to physical disabilities such as motor deficits and severe weakness). The remaining 1,136 subjects completed either the full MMSE (n 1048, 92.3% of 1,136) or, if they were visually impaired, the MMSE-blind (n 88, 7.7% of 1,136). The following analysis is based on these 1,136 participants. Vision was evaluated in a two-step procedure. First, an initial evaluation was made by means of a structured interview on sensory and motor impairment that was conducted before the cognitive test. In this interview respondents were asked, for example, if they had problems reading ordinary newspaper print or newspaper headlines. Vision impairment was assessed on the basis of self-reports given by the subjects during the structured interview using the following scale: 0—no vision impairment (unimpaired vision with glasses, small print in newspapers can be read without difficulty) 1—mild degree of vision impairment (reading possible only with considerable effort, subject tires fast, only large print such as newspaper headlines can be read without effort) 2—moderate vision impairment (people and objects can be discerned, reading with a magnifying glass only) 3—severe vision impairment (only shadows discernible, differentiation of bright and darkness, blindness) Subjects were then asked whether they could recognize vision-dependent test items of the MMSE such as the Pentagon (large figures in A4 format) during the test situation. If a vision was rated 2 or 3 on the basis of the structured interview, and if the respondents were unable to recognize vision-dependent test items, they were considered to be blind or to have low vision. In such cases the MMSE-blind was administered. In our study 88 (7.7%) out of 1,136 subjects completed the MMSE-blind due to low vision or blindness. Our assessment of vision by this two-step procedure can be considered as valid and reliable. The validity and reliability of this vision assessment are supported by three points. The rate of blindness and low vision obtained for individuals aged 75 years and older is within the range of the prevalence rates reported in other studies that are based on the standard definitions of blindness (visual acuity of less than 0.05; 20/400 in the better eye) and low vision (visual acuity of less than 0.3; 20/60 in the better eye) of the World Health Organisation [10–12]. The Baltimore Eye Survey [12], for example, reported a prevalence rate of blindness and low vision of 13.1% in a population aged 80 years and older, the Rotterdam Study [10] reported a prevalence rate of 6.0% in a population aged 75 years and older, and a study in Finland [11] found a prevalence rate of 12.0% in a population aged 70 years and older. Furthermore, no significant differences in depressive symptoms assessed by means of the CES-D (Center of Epidemiological Studies Depression Scale) [13] were found between vision-impaired and visually unimpaired subjects. It can thus be assumed that mood did not significantly influence the self-reports of vision impairment. In
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addition, a follow-up study carried out 18 months later in which the same structured interview and cognitive tests were employed confirmed the reliability of the evaluation of visual impairment. Seventy-three (83%) out of 88 visually impaired subjects were again evaluated as blind or having low vision, and 8 (9%) were found to have improved vision after successful cataract surgery. The remaining seven subjects (8%) had either died or refused to continue the study, and thus no further information could be obtained. Of the 1,048 subjects with no or only mild visual impairment 876 (83.6%) had no changes in level of vision, 80 subjects (7.6%) were blind or had low vision, and for 92 subjects (8.8%) no further information could be obtained. Test–retest reliability was found to be significant (Kappa value K 0.6) for the evaluation of visual impairment. Although we were not able to conduct ophthalmologic examinations due to the study design and the focus on dementia, we did ensure that we obtained valid and reliable information on vision impairment. The socio-demographic characteristics of the vision-impaired (n 88) and visually unimpaired (n 1,048) individuals in the sample are summarised in Table 1. The visionimpaired individuals were older (mean 86.4, SD 5.9) than those with unimpaired vision (mean 82.0, SD 5.1) (U 26319, P .000), more likely to be women (2 6.483, df 1, P .011), and had a slightly lower level of education (2 7.265, df 2, P .026). According to DSM-IV criteria, 27 (30.7%) of the subjects in the vision-impaired group were diagnosed as demented compared with 160 (15.3%) of those in the group with unimpaired vision. 2.2. Assessment and clinical diagnosis The clinical interviews were conducted by trained psychologists and physicians during visits to the subjects’ homes. The main instrument employed was the SIDAM (Structured Interview for Diagnosis of Dementia of AlzheTable 1 Socio-demographic characteristics of the sample of visually impaired (n 88) and visually unimpaired (n 1048) individuals Visually impaired (n 88) Age
Age group
Gender Education
Dementia
75–79 80–84 85 female male low middle high no information no mild moderate severe
Visually unimpaired (n 1048)
n
%
n
%
mean SD range 15 19 54 76 12 29 53 4 2 61 10 11 6
86.4 5.9 75–99 17.0 21.6 61.4 86.4 13.6 33.0 60.2 4.5 2.3 69.3 11.4 12.5 6.8
mean SD range 461 292 295 777 271 254 638 137 19 888 73 44 43
82.0 5.1 75–99 44.0 27.9 28.1 74.1 25.9 24.2 60.9 13.1 1.8 84.7 7.0 4.2 4.1
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imer-Type, Multiinfarct Dementia and Dementia of other Etiology according to the ICD-10, DSM-III-R and DSMIV) [14–16]. The SIDAM comprises a test performance part including the MMSE [17], a section for clinical judgement, and third-party information to determine psychosocial impairment. The construction of the SIDAM is based on operationalized criteria of the DSM-III-R, DSM-IV, and ICD-10. Socio-demographic data and possible risk factors for dementia were also investigated. In addition, third-party interviews were conducted, the main aim of which was to obtain information on cognitive and psychosocial functioning. Consensus conferences of physicians and psychologists were held on each subject to discuss clinical judgement and psychosocial and cognitive impairment. The clinical diagnosis of dementia was made according to DSM-IV criteria [18]. Vision-impaired study participants were administered a blind version of the MMSE (MMSE-blind) employed by Reischies and Geiselmann [2] from which all eight items involving image processing in the test situation (two items with naming, read, and obey a sentence, write a sentence, copying, and three items for performing a three-stage command) had been deleted. The number of items of the full MMSE was reduced by 27%, leaving a total possible score of 22 for the MMSE-blind (compared to a score of 30 for the full MMSE). 2.3. Statistical analysis Two procedures for interpreting the results of the MMSE-blind were examined. 2.3.1. Estimation of the full MMSE scores by linear transformation of MMSE-blind scores For the interpretation of the results of the MMSE-blind the total scores were calculated and then subjected to linear transformation [multiplication of the MMSE-blind total scores by a constant (quotient of the maximum total scores of the full MMSE and MMSE-blind: 30:22)]. The method of linear transformation requires fulfilment of some theoretical assumptions which were examined as follows. (a) Vision impairment does not influence test performance on the MMSE-blind: analysis of variance was used to test the influence of vision impairment on the total score on the MMSE-blind, controlling for age, degree of dementia, and education. In addition, the effect of vision impairment on performance on each individual item of the MMSE-blind was investigated by logistic regression analysis, controlling for the same variables as above. An alpha level of .01 was used for item assessment. (b) The test difficulty of the MMSE-blind is the same as that for the full MMSE. To compare the test difficulty of the MMSE-blind with that of the full MMSE, the percentage of correct responses to each individual MMSE item was calculated for the sample of visually unimpaired individuals. An “easier” or “more difficult” MMSEblind than the full MMSE would result in over- or underestimation of test performance by an estimated MMSE score based on linear transformation of the MMSE-blind score. (c) If the first two assumptions are met, the estimated score for the full MMSE (calculated by linear transformation of the MMSE-
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blind score) neither under- nor overestimates MMSE performance. The accuracy of the method of linear transformation can be evaluated on the basis of the MMSE performance of the visually unimpaired subjects because both an MMSE-blind score and a score for the full MMSE can be obtained for this group. The method of linear transformation was applied to the MMSE-blind scores, and the resulting estimated scores for the full MMSE were then compared to the empirical scores of the full MMSE. Under- and overestimation of MMSE performance by linear transformation of the MMSE-blind scores could then be evaluated. An estimated score of more than one point higher than the empirical MMSE score suggests overestimation of the MMSE performance by the method of linear transformation. Accordingly, an estimated score of more than one point below the empirical MMSE score suggests underestimation. The accuracies of the estimations of MMSE performance by linear transformation were evaluated for each level of cognitive functioning by calculating and comparing the proportions of accurate and inaccurate estimations. In sum, the first procedure for interpreting the results of the MMSE-blind leads to estimated scores for the full MMSE obtained by linear transformation of the MMSE-blind scores. These estimated scores can then be interpreted on the basis of existing MMSE norms (e.g., [2]). As long as there are no valid age- or education-specific reference values for the MMSEblind, the method of linear transformation appears to be the only way of interpreting the test results of visually impaired persons. The second procedure for interpreting the results of the MMSE-blind is therefore designed to establish valid ageand education-specific norms for this MMSE version. 2.3.2. Establishing norms for the MMSE-blind Analysis of variance was used to assess the effects of age, gender, and education on cognitive performance on the MMSE-blind. We studied the sensitivities and specificities of different cutoff points of the MMSE-blind for different age groups and levels of education. Sensitivity was calculated as the proportion of subjects with scores below or at a given cutoff point among those who were diagnosed as demented. Specificity was calculated as the proportion of subjects with a score above a given cutoff point among those who were diagnosed as nondemented. The data were analysed using the software package SPSS for Windows.
variables (age, education, degree of dementia) (F 1.66, P .198). The effects of vision impairment, degree of dementia, age, and education on item performance were analyzed by logistic regression analysis. At an alpha level of .01, degree of dementia had significant effects on performance on all items, age on performance on only some items. No influence of vision impairment and education on item performance was found. 3.1.2. Comparison of the test difficulty of the MMSE-blind with that of the full MMSE The frequency distributions of the items of the MMSE and MMSE-blind as functions of item difficulties are shown in Figure 1. The eight vision-dependent items that are no longer included in the MMSE-blind are all items with a low item difficulty (high percentage of correct responses between 70 and 100%). It can be assumed that the resulting MMSE-blind version, which is “more difficult” than the full MMSE, will lead to an underestimation of test performance by an estimated MMSE score based on linear transformation of the MMSE-blind score. 3.1.3. Accuracy of estimation of MMSE performance by linear transformation of the MMSE-blind score in the visually unimpaired group Table 2 summarizes the under- and overestimation of MMSE performance by estimated MMSE scores calculated by linear transformation of the MMSE-blind scores obtained for the visually unimpaired group. Comparison of the estimated and empirical scores of the full MMSE revealed that the accuracy of the estimation was very high in the lowest (total score 0–3) and highest (total score 28–30) ranges of MMSE performance. For 90.5% of subjects scoring 0–3 and 99.3% of subjects scoring 28–30 on the full MMSE, the estimated score for the full MMSE deviated not more than 1 point from the empirical MMSE score. However, at all other levels of performance the method of linear transfor-
3. Results 3.1. Estimation of the full MMSE scores by linear transformation of MMSE-blind scores The assumptions of the method of linear transformation of scores are met as follows. 3.1.1. Influence of vision impairment on test performance on the MMSE-blind No influence of vision impairment was found on the MMSE-blind total score after controlling for other relevant
Fig. 1. The frequency distributions of the items of the MMSE and MMSEblind as a function of the item difficulties.
A. Busse et al. / Journal of Clinical Epidemiology 55 (2002) 909–915 Table 2 Accuracy of estimated compared to empirical scores on the full MMSE in visually unimpaired subjects
Number of cases underestimateda
Number of cases accurately estimatedb
Number of cases overestimatedc
n (%)
n (%)
n (%)
n (%)
21 (100.0) 15 (100.0) 11 (100.0) 12 (100.0) 17 (100.0) 24 (100.0) 47 (100.0) 128 (100.0) 362 (100.0) 411 (100.0) 1048 (100.0)
0 (0.0) 9 (60.0) 8 (72.7) 11 (91.7) 10 (58.8) 19 (79.2) 22 (46.8) 51 (39.8) 162 (44.8) 0 (0.0) 292 (27.9)
19 (90.5) 3 (20.0) 3 (27.3) 1 (8.3) 6 (35.3) 4 (16.7) 25 (53.2) 68 (53.1) 174 (48.1) 408 (99.3) 711 (67.8)
2 (9.5) 3 (20.0) 0 (0.0) 0 (0.0) 1 (5.9) 1 (4.2) 0 (0.0) 9 (7.0) 26 (7.2) 3 (0.7) 45 (4.3)
Empirical score of the full MMSE
Number of cases
0–3 4–6 7–9 10–12 13–15 16–18 19–21 22–24 25–27 28–30 Total
a The estimated score for the full MMSE by linear transformation of the MMSE -blind score is more than one point below the empirical score of the full MMSE. b The deviation of the estimated score is not greater than 1 point of the empirical score of the full MMSE . c The estimated score for the full MMSE by linear transformation of the MMSE -blind score is more than one point higher than the empirical score of the full MMSE.
mation resulted in a clear underestimation of cognitive performance. For example, linear transformation of the MMSE-blind scores led to an underestimation of the actual test performance of almost 40% of subjects scoring 22–24 on the full MMSE. In contrast, hardly any overestimations of scores resulted from linear transformation of the MMSEblind scores. 3.2. Establishing norms for the MMSE-blind Table 3 gives the age-and education-specific norms for the MMSE-blind established for all vision-impaired and vision-unimpaired subjects (n 1,133 of 1,136 subjects; the levels of education of three nondemented participants were unknown). Age (F 8.6, P .000) and education (F 12.6, P .000) had an independent effect on MMSE-blind performance, whereas sex did not influence performance (F 2.1, P .149). Significant differences were found between the mean MMSE-blind scores of subjects at all levels of education in all three age groups (75–79, 80–84, 85). The percentile ranks for the MMSE-blind scores, the sensitivities and specificities for different cutoff points used to discriminate between demented and nondemented individuals for each age group, and level of education are given in Table 3. The recommended cutoff points vary from 15 to 17, depending on age and level of education. All cutoff points have a high sensitivity (between 91 and 100%) and specificity (between 80 and 100%). Test–retest reliability for the MMSE-blind was assessed in a sample of 35 subjects aged 75 years and older. It was carried out within a 2-weeks interval. We applied the kappa
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statistics and obtained a significant K value of 0.5. Increased scores on retest were found (Wilcoxon-test, z 2.43, P .015) presumably due to practice effects. 4. Discussion As indicated by the results of other studies [6,7], the proportion of dementia cases in our sample was higher in the group of vision-impaired individuals than in those with unimpaired vision. The group of vision-impaired individuals was also significantly older, and therefore, had a higher risk of dementia than the vision-unimpaired group. This emphasises the importance of including vision-impaired individuals in epidemiologic studies and of employing a valid assessment of cognitive functioning. Moreover, in clinical practice it is important to have a valid screening instrument for detecting dementia in vision-impaired older persons. The MMSE-blind can be used to assess orientation to time and place, memory, attention, calculation, and language. These areas of cognitive functioning have been found to have discriminative power in the detection of dementia [19–23]. This article has examined two procedures of interpreting results of the MMSE with missing values due to vision impairment. Use of the method of linear transformation to estimate a full MMSE score derived from the MMSE-blind score resulted mainly in an underestimation of cognitive performance. Underestimation of cognitive functioning could result in an unjustified diagnosis of dementia. This is in line with the results of a study by Jagger et al. [3], which indicated that cognitively impaired individuals with poor vision are more likely to be diagnosed as demented or are assessed as having more severe dementia. Because not all the assumptions required for performing linear transformation of the scores were met, this procedure should not be given priority. Moreover, Fichter et al. [8] reported that estimating scores did not lead to an accurate assessment of cognitive functioning. Because impaired vision had no significant influence on item performance on the MMSE-blind introduced by Reischies and Geiselmann [2], no further item was omitted from the present version of the test. Our cutoff points were lower than those suggested by Reischies and Geiselmann [2], which confirms their assumption that their cutoffs are rather high (18–19 for age group 70–84 and 16–17 for age group 85). The validity of the MMSE-blind is comparable to that reported for the full MMSE (e.g., [24]). Consequently, this test version can be recommended in the event that vision-impaired individuals need to be tested and their vision is not sufficiently improved by the provision of large print and pictures or optical aids. It can also be useful for assessing subjects with a motor impairment or considerable weakness. However, the MMSE-blind should not be considered a substitute for the full MMSE. Because there are qualitative differences in cognitive impairment in individuals with different types of dementia [19], abbreviated forms that do not
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Table 3 MMSE-blind: age- and education-specific norms (percentile ranks) Nondemented participants
Total score 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
mean: (SD): Range: Recommended cutoff points (sensitivity/ specificity)
Age group 75–79
Age group 80–84
Age group 85
Education
Education
Education
low (n 88)
1 5 17 28 44 73 89 100
19.4 (1.7)
middle (n 279)
1 3 8 20 34 56 84 100
20.0 (1.6)
high (n 86)
1 6 15 36 65 100
20.8 (1.2)
low (n 52)
2 2 2 4 14 25 39 67 85 94 100
18.7 (1.9)
middle (n 182)
1 2 6 14 25 45 71 86 100
high (n 27)
4 4 19 33 52 78 100
19.5
20.1
(1.7)
(1.6)
low (n 66)
2 2 3 3 14 30 58 71 91 97 100
18.3 (1.8)
middle (n 145)
1 1 1 4 10 21 39 59 83 93 100
18.9 (1.8)
high (n 21)
14 24 38 67 86 100
19.7 (1.6)
15-22
15-22
17-22
12-22
14-22
16-22
12-22
12-22
17-22
16
16
17
15
16
17
15
16
16
99/95
99/97
91/96
99/94
91/97
99/80
99/100
100/99
assess certain neuropsychologic syndromes can fail to detect certain types of dementia. Consequently, when administration of the full MMSE and further neuropsychologic testing are possible, the full version should be given priority. Our preliminary study has some limitations that could be addressed by future studies. The evaluation of vision impairment was not based on ophthalmologic examination, which was not possible within the framework of our population-based study. However, the fact that our prevalence rates of blindness and low vision are comparable with those found by other studies [10–12], and that self-reporting of vision impairment was not influenced by depressed mood and remained relatively stable over time underlines the reliability and the validity of our assessment. A further limitation is that the clinical diagnosis of dementia was not made without knowledge of the MMSE score. However, the MMSE score played only a small part in the establishment of the di-
100/96
Demented participants (n 187) 10 12 16 21 23 27 31 36 39 42 51 56 65 70 81 91 99 100 100
mild: 13.9 (1.8) moderate: 8.9 (2.7) severe: 2.1 (2.2)
agnosis, being administered in addition to a full cognitive test carried out as part of the SIDAM, which also included clinical judgement, third party information, and an evaluation of the extent to which cognitive impairment interfered with psychosocial functioning. Despite these limitations, the MMSE-blind seems to be a valid instrument that permits wider application of the MMSE in old age, both for epidemiologic studies and in clinical practice. The adaptation of dementia screening for vision-impaired older persons has proved to be a successful way of obtaining valid results of cognitive functioning. Our results have the following implications for the adaptation of screening instruments with vision-dependent items for vision-impaired older persons in general. (1) Age- and education-specific norms for the blind version should be developed to provide a valid basis for the interpretation of the test results. (2) If it is not possible to establish norms for a blind version, the
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method of linear transformation of scores on the blind version can be applied to estimate the scores for the full test version. However, estimated scores should be interpreted with caution because they may over- or underestimate cognitive functioning. To assess possible errors of estimation the item difficulties of the original and blind versions can be compared. An “easier” or “more difficult” blind version than the original test version would result in over- or underestimation of test performance. Acknowledgments This article was supported by the German Bundesministerium für Bildung und Forschung (BMBF), Interdisciplinary Centre for Clinical Research (IZKF) at the University of Leipzig (01KS9504, Projekt C7 79934700). We would also like to thank the anonymous reviewers for their helpul comments on earlier drafts.
References [1] Launer LJ, Dinkgreve MA, Jonker C, Hooijer C, Lindeboom J. Are age and education independent correlates of the Mini-Mental State Exam performance of community-dwelling elderly? J Gerontol 1993; 48(6):271–7. [2] Reischies FM, Geiselmann B. Age-related cognitive decline and vision impairment affecting the detection of dementia syndrome in old age. Br J Psychiatry 1997;171:449–51. [3] Jagger C, Clarke M, Anderson J, Battcock T. Misclassification of dementia by the Mini-Mental State Examination—are education and social class the only factors? Age Ageing 1992;21:404–11. [4] Cosi V, Citterio A, Ratti MT, Romani A. Pavia memory project: study design and first results. Ital J Neurol Sci 1995;16:141–8. [5] Korten AE, Henderson AS, Christensen H, Jorm AF, Rodgers B, Jacomb P, Mackinnon AJ. A prospective study of cognitive function in the elderly. Psychol Med 1997;27:919–30. [6] Riedel-Heller SG, Busse A, Angermeyer MC. Are cognitively impaired individuals adequately represented in community surveys? Recruitment challenges and strategies to facilitate participation in community surveys of older adults. A review. Eur J Epidemiol 2000;16:827–35. [7] Uhlmann RF, Larson EB, Koepsell TD, Rees TS, Duckert LG. Visual impairment and cognitive dysfunction in Alzheimer’s disease. J Gen Intern Med 1991;6(2):126–32. [8] Fichter MM, Meller I, Schroeppel H, Steinkirchner R. Dementia and cognitive impairment in the oldest old in the community. Prevalence and comorbidity. Br J Psychiatry 1995;166:621–9.
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[9] Riedel-Heller SG, Schork A, Matschinger H, Angermeyer MC. Recruitment procedures and their impact on the prevalence of dementia: results from the Leipzig Longitudinal Study of the Aged (LEILA75). Neuroepidemiology 2000;19:130–40. [10] Klaver CC, Wolfs RC, Vingerling JR, Hofman A, de Jong PT. Agespecific prevalence and causes of blindness and visual impairment in an older population: the Rotterdam Study. Arch Ophthalmol 1998; 116:653–8. [11] Hirvela H, Laatikainen L. Visual acuity in a population aged 70 years or older; prevalence and causes of visual impairment. Acta Ophthalmol Scand 1995;73(2):99–104. [12] Tielsch JM, Sommer A, Witt K, Katz J, Royall RM. The Baltimore Eye Survey Research Group. Blindness and visual impairment in an American urban population: The Baltimore Eye Survey. Arch Ophthalmol 1990;108:286–90. [13] Radloff LS. The CES-D Scale: a selfrReport depression scale for research in the general population. Appl Psychol Measure 1977;1(3):385–401. [14] Zaudig M, Mittelhammer J, Hiller W. SIDAM- Strukturiertes Interview für die Diagnose der Demenz vom Alzheimer Typ, der Multiinfarkt-Demenz und Demenzen anderer Ätiologie nach DSM-III-R und ICD-10-Manual. München: Logomed; 1990. [15] Zaudig M, Mittelhammer J, Hiller W, Pauls A, Thora C, Morinigo A, Mombour W. SIDAM: a structured interview for the diagnosis of dementia of the Alzheimer type, multi-infarct dementia and dementias of other aetiology according to ICD-10 and DSM-III-R. Psychol Med 1991;21:225–36. [16] Zaudig M. A new systematic method of measurement and diagnosis of “mild cognitive impairment” and dementia according to ICD-10 and DSM-III-R criteria. Int Psychogeriatr 1992;4(2):203–19. [17] Folstein MF, Folstein SE, McHugh PR. Mini-Mental-State: a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 1975;12:189–98. [18] American Psychiatric Association. Diagnostic and statistical manual of mental disorders DSM-IV. 4th ed. Washington, DC: APA; 1994. [19] Pasquier F. Early diagnosis of dementia: neuropsychology. J Neurol 1999;246:6–15. [20] Collie A, Maruff P. The neuropsychology of pre-clinical Alzheimer’s disease and mild cognitive impairment. Neurosci Biobehav Rev 2000;24:365–74. [21] Commenges D, Gagnon M, Letenneur L, Dartigues JF, BarbergerGateau P, Salamon R. Improving screening for dementia in the elderly using Mini-Mental State Examination subscores, Benton’s Visual Retention Test, and Isaacs’ Set Test. Epidemiology 1992;3(2):185–8. [22] Fabrigoule C, Rouch I, Taberly A, Letenneur L, Commenges D, Mazaux JM, Orgogozo JM, Dartigues JF. Cognitive process in preclinical phase of dementia. Brain 1998;121:135–41. [23] Masur DM, Sliwinski M, Lipton RB, Blau AD, Crystal HA. Neuropsychological prediction of dementia and the absence of dementia in healthy elderly persons. Neurology 1994;44:1427–32. [24] Tombaugh TN, McIntyre NJ. The Mini-Mental State Examination: a comprehensive review. J Am Geriatr Soc 1992;40:922–35.
Adaptation of dementia screening for vision-impaired older persons Administration of the Mini-Mental State Examination (MMSE) Anja Busse*, Astrid Sonntag, Jeannette Bischkopf, Herbert Matschinger, Matthias C. Angermeyer Klinik und Poliklinik für Psychiatrie der Universität Leipzig, Johannisallee 20, 04317 Leipzig, Germany Received 20 August 2000; received in revised form 13 March 2001; accepted 24 April 2002
Abstract In epidemiologic field studies on the prevalence and incidence of dementia the problems associated with the cognitive testing of visually impaired individuals are rarely discussed. In the Leipzig Longitudinal Study of the Aged (LEILA 75) a version of the Mini-Mental State Examination for the visually impaired (MMSE-blind) was employed from which all items requiring image processing had been omitted. To be able to interpret the test results and include vision-impaired individuals in the field study, the scores for the full MMSE were estimated by conducting linear transformation of the scores obtained on the MMSE-blind. The method of linear transformation is based on certain theoretical assumptions that are examined in this article. Linear transformation of scores has proved to be a valid procedure only for individuals with very high or very low cognitive performance. Thus, evaluation of the estimated full MMSE scores based on the norms for the original MMSE is not recommended. A blind version of the MMSE with age- and education-specific norms that has been validated as a screening tool for dementia is therefore presented. © 2002 Elsevier Science Inc. All rights reserved. Keywords: Dementia; MMSE; Visual impairment; Norms; Validity
1. Introduction Vision impairment, a common phenomenon in old age, leads to problems with cognitive testing and the detection of dementia in old people [1–3]. Vision-impaired individuals are often unable to respond to test items requiring image processing. Resulting missing values in cognitive tests lead to difficulties in interpreting test results. Screening instruments for detecting dementia whose items are partly vision dependent thus need to be adapted for administration to visionimpaired individuals. This raises the question as to whether such adapted tests lead to a valid diagnosis or whether they lose discriminative power in the detection of dementia [2]. The problem of vision impairment in the detection of dementia is rarely discussed in the literature. Epidemiologic studies on the prevalence and incidence of dementia hardly mention this problem. Some studies have excluded individuals with sensory impairment as ”not testable,” or have not interpreted their test results [4,5], which fails to take into account the fact that there may be a higher proportion of dementia cases in this group of individuals [6,7]. Other studies have estimated miss* Corresponding author. Tel.: 0341/97 24 530; fax: 0341/97 24 539. E-mail address: [email protected] (A. Busse).
ing responses on the basis of valid responses [5,8], thus establishing a procedure for integrating vision-impaired subjects in epidemiologic studies. However, these studies did not always investigate whether assessments of cognitive functioning based on this estimation of scores are, in fact, valid. Reischies and Geiselmann [2] reported that omitting vision-dependent MMSE items does not reduce the discriminative power of the MMSE (Mini-Mental State Examination). Neither the sensitivity nor the specificity of their version of the MMSE for the visually impaired was lower than those of the full MMSE. However, the authors of this study found that their cutoffs for the original MMSE were ”higher than in comparable epidemiological studies” and their ”values for sensitivity and specificity . . . slightly lower than those reported in the literature.” The reported reasons for these results may also have influenced the cutoffs of the MMSE version for the visually impaired. Norms for this MMSE version were presented only for different age groups, and effects of education were not analyzed. Moreover, the question as to whether the process of responding to items of the blind version is truly independent of vision impairment was not addressed. Although understanding and answering an item in the test situation may not require image processing, the ability to process images in everyday life could affect a person’s knowledge of certain facts or events. Vision-impaired people
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are, for example, unable to read newspapers or calendars, and may thus be less likely to know the date. Items that are not independent of vision in this sense should be excluded from a blind version of a screening test because they lack discriminative power in detecting dementia. In sum, recent studies have introduced two possible procedures for including vision-impaired subjects in epidemiologic studies: first, estimation of missing values on the basis of valid responses, and second, omission of all vision-dependent items from the test and establishment of norms for a reduced test version for vision-impaired people. Taking the MMSE as an example, this article aims to answer the following questions regarding these two procedures: (1) is the estimation of full MMSE scores a valid method for examining and interpreting cognitive performance with the aid of screening instruments that include vision-dependent items, such as the MMSE? (2) Are responses to the items of the blind version of the MMSE introduced by Reischies and Geiselmann (1997) [2] in fact unaffected by vision impairment? (3) Does the MMSE retain its validity when all items are omitted that require (direct and indirect) image processing to make a blind version? To date, the problem of vision impairment in the detection of dementia has remained unsolved. The aim of the following study is to contribute to the assessment and diagnosis of vision-impaired older persons in both epidemiologic studies and clinical practice.
2. Methods 2.1. Subjects The data were derived from the baseline assessment of a population-based study on the epidemiology of dementia (Leipzig Longitudinal Study of the Aged, LEILA 75) carried out from January 1997 to June 1998. A total of 1,500 community-dwelling individuals aged 75 and over and resident in the Leipzig-South district, Germany, were identified by systematic random sampling from an age-ordered list provided by the local registry office. Institutionalized individuals were included in the study on a proportional basis (n 192). The study design of the Leipzig Longitudinal Study of the Aged has been described in detail elsewhere [9]. Of the overall sample of 1,692 subjects, 242 (14.2%) declined to participate, 57 (3.4%) had died, and 15 (0.9%) were not traceable. Information on 113 (6.7%) study subjects who were shielded by their relatives was obtained solely by proxy interviews. Clinical interviews incorporating neuropsychologic assessment (including the MMSE) were conducted with 1,265 (74.8%) participants. These 1,265 study subjects did not differ significantly from the remainder of the sample in regard to age (U 263,553, P .455), gender (2 0.391, df 1, P .532) or marital status (2 5.027, df 3, P .170). The results of the cognitive tests of 22 participants with mental retardation or other psychiatric disorders were excluded. A further 107 subjects were excluded from the analysis for other reasons (i.e., because too little was known about the quality
of their vision or because an abridged version of the MMSE version had been administered owing to physical disabilities such as motor deficits and severe weakness). The remaining 1,136 subjects completed either the full MMSE (n 1048, 92.3% of 1,136) or, if they were visually impaired, the MMSE-blind (n 88, 7.7% of 1,136). The following analysis is based on these 1,136 participants. Vision was evaluated in a two-step procedure. First, an initial evaluation was made by means of a structured interview on sensory and motor impairment that was conducted before the cognitive test. In this interview respondents were asked, for example, if they had problems reading ordinary newspaper print or newspaper headlines. Vision impairment was assessed on the basis of self-reports given by the subjects during the structured interview using the following scale: 0—no vision impairment (unimpaired vision with glasses, small print in newspapers can be read without difficulty) 1—mild degree of vision impairment (reading possible only with considerable effort, subject tires fast, only large print such as newspaper headlines can be read without effort) 2—moderate vision impairment (people and objects can be discerned, reading with a magnifying glass only) 3—severe vision impairment (only shadows discernible, differentiation of bright and darkness, blindness) Subjects were then asked whether they could recognize vision-dependent test items of the MMSE such as the Pentagon (large figures in A4 format) during the test situation. If a vision was rated 2 or 3 on the basis of the structured interview, and if the respondents were unable to recognize vision-dependent test items, they were considered to be blind or to have low vision. In such cases the MMSE-blind was administered. In our study 88 (7.7%) out of 1,136 subjects completed the MMSE-blind due to low vision or blindness. Our assessment of vision by this two-step procedure can be considered as valid and reliable. The validity and reliability of this vision assessment are supported by three points. The rate of blindness and low vision obtained for individuals aged 75 years and older is within the range of the prevalence rates reported in other studies that are based on the standard definitions of blindness (visual acuity of less than 0.05; 20/400 in the better eye) and low vision (visual acuity of less than 0.3; 20/60 in the better eye) of the World Health Organisation [10–12]. The Baltimore Eye Survey [12], for example, reported a prevalence rate of blindness and low vision of 13.1% in a population aged 80 years and older, the Rotterdam Study [10] reported a prevalence rate of 6.0% in a population aged 75 years and older, and a study in Finland [11] found a prevalence rate of 12.0% in a population aged 70 years and older. Furthermore, no significant differences in depressive symptoms assessed by means of the CES-D (Center of Epidemiological Studies Depression Scale) [13] were found between vision-impaired and visually unimpaired subjects. It can thus be assumed that mood did not significantly influence the self-reports of vision impairment. In
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addition, a follow-up study carried out 18 months later in which the same structured interview and cognitive tests were employed confirmed the reliability of the evaluation of visual impairment. Seventy-three (83%) out of 88 visually impaired subjects were again evaluated as blind or having low vision, and 8 (9%) were found to have improved vision after successful cataract surgery. The remaining seven subjects (8%) had either died or refused to continue the study, and thus no further information could be obtained. Of the 1,048 subjects with no or only mild visual impairment 876 (83.6%) had no changes in level of vision, 80 subjects (7.6%) were blind or had low vision, and for 92 subjects (8.8%) no further information could be obtained. Test–retest reliability was found to be significant (Kappa value K 0.6) for the evaluation of visual impairment. Although we were not able to conduct ophthalmologic examinations due to the study design and the focus on dementia, we did ensure that we obtained valid and reliable information on vision impairment. The socio-demographic characteristics of the vision-impaired (n 88) and visually unimpaired (n 1,048) individuals in the sample are summarised in Table 1. The visionimpaired individuals were older (mean 86.4, SD 5.9) than those with unimpaired vision (mean 82.0, SD 5.1) (U 26319, P .000), more likely to be women (2 6.483, df 1, P .011), and had a slightly lower level of education (2 7.265, df 2, P .026). According to DSM-IV criteria, 27 (30.7%) of the subjects in the vision-impaired group were diagnosed as demented compared with 160 (15.3%) of those in the group with unimpaired vision. 2.2. Assessment and clinical diagnosis The clinical interviews were conducted by trained psychologists and physicians during visits to the subjects’ homes. The main instrument employed was the SIDAM (Structured Interview for Diagnosis of Dementia of AlzheTable 1 Socio-demographic characteristics of the sample of visually impaired (n 88) and visually unimpaired (n 1048) individuals Visually impaired (n 88) Age
Age group
Gender Education
Dementia
75–79 80–84 85 female male low middle high no information no mild moderate severe
Visually unimpaired (n 1048)
n
%
n
%
mean SD range 15 19 54 76 12 29 53 4 2 61 10 11 6
86.4 5.9 75–99 17.0 21.6 61.4 86.4 13.6 33.0 60.2 4.5 2.3 69.3 11.4 12.5 6.8
mean SD range 461 292 295 777 271 254 638 137 19 888 73 44 43
82.0 5.1 75–99 44.0 27.9 28.1 74.1 25.9 24.2 60.9 13.1 1.8 84.7 7.0 4.2 4.1
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imer-Type, Multiinfarct Dementia and Dementia of other Etiology according to the ICD-10, DSM-III-R and DSMIV) [14–16]. The SIDAM comprises a test performance part including the MMSE [17], a section for clinical judgement, and third-party information to determine psychosocial impairment. The construction of the SIDAM is based on operationalized criteria of the DSM-III-R, DSM-IV, and ICD-10. Socio-demographic data and possible risk factors for dementia were also investigated. In addition, third-party interviews were conducted, the main aim of which was to obtain information on cognitive and psychosocial functioning. Consensus conferences of physicians and psychologists were held on each subject to discuss clinical judgement and psychosocial and cognitive impairment. The clinical diagnosis of dementia was made according to DSM-IV criteria [18]. Vision-impaired study participants were administered a blind version of the MMSE (MMSE-blind) employed by Reischies and Geiselmann [2] from which all eight items involving image processing in the test situation (two items with naming, read, and obey a sentence, write a sentence, copying, and three items for performing a three-stage command) had been deleted. The number of items of the full MMSE was reduced by 27%, leaving a total possible score of 22 for the MMSE-blind (compared to a score of 30 for the full MMSE). 2.3. Statistical analysis Two procedures for interpreting the results of the MMSE-blind were examined. 2.3.1. Estimation of the full MMSE scores by linear transformation of MMSE-blind scores For the interpretation of the results of the MMSE-blind the total scores were calculated and then subjected to linear transformation [multiplication of the MMSE-blind total scores by a constant (quotient of the maximum total scores of the full MMSE and MMSE-blind: 30:22)]. The method of linear transformation requires fulfilment of some theoretical assumptions which were examined as follows. (a) Vision impairment does not influence test performance on the MMSE-blind: analysis of variance was used to test the influence of vision impairment on the total score on the MMSE-blind, controlling for age, degree of dementia, and education. In addition, the effect of vision impairment on performance on each individual item of the MMSE-blind was investigated by logistic regression analysis, controlling for the same variables as above. An alpha level of .01 was used for item assessment. (b) The test difficulty of the MMSE-blind is the same as that for the full MMSE. To compare the test difficulty of the MMSE-blind with that of the full MMSE, the percentage of correct responses to each individual MMSE item was calculated for the sample of visually unimpaired individuals. An “easier” or “more difficult” MMSEblind than the full MMSE would result in over- or underestimation of test performance by an estimated MMSE score based on linear transformation of the MMSE-blind score. (c) If the first two assumptions are met, the estimated score for the full MMSE (calculated by linear transformation of the MMSE-
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blind score) neither under- nor overestimates MMSE performance. The accuracy of the method of linear transformation can be evaluated on the basis of the MMSE performance of the visually unimpaired subjects because both an MMSE-blind score and a score for the full MMSE can be obtained for this group. The method of linear transformation was applied to the MMSE-blind scores, and the resulting estimated scores for the full MMSE were then compared to the empirical scores of the full MMSE. Under- and overestimation of MMSE performance by linear transformation of the MMSE-blind scores could then be evaluated. An estimated score of more than one point higher than the empirical MMSE score suggests overestimation of the MMSE performance by the method of linear transformation. Accordingly, an estimated score of more than one point below the empirical MMSE score suggests underestimation. The accuracies of the estimations of MMSE performance by linear transformation were evaluated for each level of cognitive functioning by calculating and comparing the proportions of accurate and inaccurate estimations. In sum, the first procedure for interpreting the results of the MMSE-blind leads to estimated scores for the full MMSE obtained by linear transformation of the MMSE-blind scores. These estimated scores can then be interpreted on the basis of existing MMSE norms (e.g., [2]). As long as there are no valid age- or education-specific reference values for the MMSEblind, the method of linear transformation appears to be the only way of interpreting the test results of visually impaired persons. The second procedure for interpreting the results of the MMSE-blind is therefore designed to establish valid ageand education-specific norms for this MMSE version. 2.3.2. Establishing norms for the MMSE-blind Analysis of variance was used to assess the effects of age, gender, and education on cognitive performance on the MMSE-blind. We studied the sensitivities and specificities of different cutoff points of the MMSE-blind for different age groups and levels of education. Sensitivity was calculated as the proportion of subjects with scores below or at a given cutoff point among those who were diagnosed as demented. Specificity was calculated as the proportion of subjects with a score above a given cutoff point among those who were diagnosed as nondemented. The data were analysed using the software package SPSS for Windows.
variables (age, education, degree of dementia) (F 1.66, P .198). The effects of vision impairment, degree of dementia, age, and education on item performance were analyzed by logistic regression analysis. At an alpha level of .01, degree of dementia had significant effects on performance on all items, age on performance on only some items. No influence of vision impairment and education on item performance was found. 3.1.2. Comparison of the test difficulty of the MMSE-blind with that of the full MMSE The frequency distributions of the items of the MMSE and MMSE-blind as functions of item difficulties are shown in Figure 1. The eight vision-dependent items that are no longer included in the MMSE-blind are all items with a low item difficulty (high percentage of correct responses between 70 and 100%). It can be assumed that the resulting MMSE-blind version, which is “more difficult” than the full MMSE, will lead to an underestimation of test performance by an estimated MMSE score based on linear transformation of the MMSE-blind score. 3.1.3. Accuracy of estimation of MMSE performance by linear transformation of the MMSE-blind score in the visually unimpaired group Table 2 summarizes the under- and overestimation of MMSE performance by estimated MMSE scores calculated by linear transformation of the MMSE-blind scores obtained for the visually unimpaired group. Comparison of the estimated and empirical scores of the full MMSE revealed that the accuracy of the estimation was very high in the lowest (total score 0–3) and highest (total score 28–30) ranges of MMSE performance. For 90.5% of subjects scoring 0–3 and 99.3% of subjects scoring 28–30 on the full MMSE, the estimated score for the full MMSE deviated not more than 1 point from the empirical MMSE score. However, at all other levels of performance the method of linear transfor-
3. Results 3.1. Estimation of the full MMSE scores by linear transformation of MMSE-blind scores The assumptions of the method of linear transformation of scores are met as follows. 3.1.1. Influence of vision impairment on test performance on the MMSE-blind No influence of vision impairment was found on the MMSE-blind total score after controlling for other relevant
Fig. 1. The frequency distributions of the items of the MMSE and MMSEblind as a function of the item difficulties.
A. Busse et al. / Journal of Clinical Epidemiology 55 (2002) 909–915 Table 2 Accuracy of estimated compared to empirical scores on the full MMSE in visually unimpaired subjects
Number of cases underestimateda
Number of cases accurately estimatedb
Number of cases overestimatedc
n (%)
n (%)
n (%)
n (%)
21 (100.0) 15 (100.0) 11 (100.0) 12 (100.0) 17 (100.0) 24 (100.0) 47 (100.0) 128 (100.0) 362 (100.0) 411 (100.0) 1048 (100.0)
0 (0.0) 9 (60.0) 8 (72.7) 11 (91.7) 10 (58.8) 19 (79.2) 22 (46.8) 51 (39.8) 162 (44.8) 0 (0.0) 292 (27.9)
19 (90.5) 3 (20.0) 3 (27.3) 1 (8.3) 6 (35.3) 4 (16.7) 25 (53.2) 68 (53.1) 174 (48.1) 408 (99.3) 711 (67.8)
2 (9.5) 3 (20.0) 0 (0.0) 0 (0.0) 1 (5.9) 1 (4.2) 0 (0.0) 9 (7.0) 26 (7.2) 3 (0.7) 45 (4.3)
Empirical score of the full MMSE
Number of cases
0–3 4–6 7–9 10–12 13–15 16–18 19–21 22–24 25–27 28–30 Total
a The estimated score for the full MMSE by linear transformation of the MMSE -blind score is more than one point below the empirical score of the full MMSE. b The deviation of the estimated score is not greater than 1 point of the empirical score of the full MMSE . c The estimated score for the full MMSE by linear transformation of the MMSE -blind score is more than one point higher than the empirical score of the full MMSE.
mation resulted in a clear underestimation of cognitive performance. For example, linear transformation of the MMSE-blind scores led to an underestimation of the actual test performance of almost 40% of subjects scoring 22–24 on the full MMSE. In contrast, hardly any overestimations of scores resulted from linear transformation of the MMSEblind scores. 3.2. Establishing norms for the MMSE-blind Table 3 gives the age-and education-specific norms for the MMSE-blind established for all vision-impaired and vision-unimpaired subjects (n 1,133 of 1,136 subjects; the levels of education of three nondemented participants were unknown). Age (F 8.6, P .000) and education (F 12.6, P .000) had an independent effect on MMSE-blind performance, whereas sex did not influence performance (F 2.1, P .149). Significant differences were found between the mean MMSE-blind scores of subjects at all levels of education in all three age groups (75–79, 80–84, 85). The percentile ranks for the MMSE-blind scores, the sensitivities and specificities for different cutoff points used to discriminate between demented and nondemented individuals for each age group, and level of education are given in Table 3. The recommended cutoff points vary from 15 to 17, depending on age and level of education. All cutoff points have a high sensitivity (between 91 and 100%) and specificity (between 80 and 100%). Test–retest reliability for the MMSE-blind was assessed in a sample of 35 subjects aged 75 years and older. It was carried out within a 2-weeks interval. We applied the kappa
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statistics and obtained a significant K value of 0.5. Increased scores on retest were found (Wilcoxon-test, z 2.43, P .015) presumably due to practice effects. 4. Discussion As indicated by the results of other studies [6,7], the proportion of dementia cases in our sample was higher in the group of vision-impaired individuals than in those with unimpaired vision. The group of vision-impaired individuals was also significantly older, and therefore, had a higher risk of dementia than the vision-unimpaired group. This emphasises the importance of including vision-impaired individuals in epidemiologic studies and of employing a valid assessment of cognitive functioning. Moreover, in clinical practice it is important to have a valid screening instrument for detecting dementia in vision-impaired older persons. The MMSE-blind can be used to assess orientation to time and place, memory, attention, calculation, and language. These areas of cognitive functioning have been found to have discriminative power in the detection of dementia [19–23]. This article has examined two procedures of interpreting results of the MMSE with missing values due to vision impairment. Use of the method of linear transformation to estimate a full MMSE score derived from the MMSE-blind score resulted mainly in an underestimation of cognitive performance. Underestimation of cognitive functioning could result in an unjustified diagnosis of dementia. This is in line with the results of a study by Jagger et al. [3], which indicated that cognitively impaired individuals with poor vision are more likely to be diagnosed as demented or are assessed as having more severe dementia. Because not all the assumptions required for performing linear transformation of the scores were met, this procedure should not be given priority. Moreover, Fichter et al. [8] reported that estimating scores did not lead to an accurate assessment of cognitive functioning. Because impaired vision had no significant influence on item performance on the MMSE-blind introduced by Reischies and Geiselmann [2], no further item was omitted from the present version of the test. Our cutoff points were lower than those suggested by Reischies and Geiselmann [2], which confirms their assumption that their cutoffs are rather high (18–19 for age group 70–84 and 16–17 for age group 85). The validity of the MMSE-blind is comparable to that reported for the full MMSE (e.g., [24]). Consequently, this test version can be recommended in the event that vision-impaired individuals need to be tested and their vision is not sufficiently improved by the provision of large print and pictures or optical aids. It can also be useful for assessing subjects with a motor impairment or considerable weakness. However, the MMSE-blind should not be considered a substitute for the full MMSE. Because there are qualitative differences in cognitive impairment in individuals with different types of dementia [19], abbreviated forms that do not
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Table 3 MMSE-blind: age- and education-specific norms (percentile ranks) Nondemented participants
Total score 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
mean: (SD): Range: Recommended cutoff points (sensitivity/ specificity)
Age group 75–79
Age group 80–84
Age group 85
Education
Education
Education
low (n 88)
1 5 17 28 44 73 89 100
19.4 (1.7)
middle (n 279)
1 3 8 20 34 56 84 100
20.0 (1.6)
high (n 86)
1 6 15 36 65 100
20.8 (1.2)
low (n 52)
2 2 2 4 14 25 39 67 85 94 100
18.7 (1.9)
middle (n 182)
1 2 6 14 25 45 71 86 100
high (n 27)
4 4 19 33 52 78 100
19.5
20.1
(1.7)
(1.6)
low (n 66)
2 2 3 3 14 30 58 71 91 97 100
18.3 (1.8)
middle (n 145)
1 1 1 4 10 21 39 59 83 93 100
18.9 (1.8)
high (n 21)
14 24 38 67 86 100
19.7 (1.6)
15-22
15-22
17-22
12-22
14-22
16-22
12-22
12-22
17-22
16
16
17
15
16
17
15
16
16
99/95
99/97
91/96
99/94
91/97
99/80
99/100
100/99
assess certain neuropsychologic syndromes can fail to detect certain types of dementia. Consequently, when administration of the full MMSE and further neuropsychologic testing are possible, the full version should be given priority. Our preliminary study has some limitations that could be addressed by future studies. The evaluation of vision impairment was not based on ophthalmologic examination, which was not possible within the framework of our population-based study. However, the fact that our prevalence rates of blindness and low vision are comparable with those found by other studies [10–12], and that self-reporting of vision impairment was not influenced by depressed mood and remained relatively stable over time underlines the reliability and the validity of our assessment. A further limitation is that the clinical diagnosis of dementia was not made without knowledge of the MMSE score. However, the MMSE score played only a small part in the establishment of the di-
100/96
Demented participants (n 187) 10 12 16 21 23 27 31 36 39 42 51 56 65 70 81 91 99 100 100
mild: 13.9 (1.8) moderate: 8.9 (2.7) severe: 2.1 (2.2)
agnosis, being administered in addition to a full cognitive test carried out as part of the SIDAM, which also included clinical judgement, third party information, and an evaluation of the extent to which cognitive impairment interfered with psychosocial functioning. Despite these limitations, the MMSE-blind seems to be a valid instrument that permits wider application of the MMSE in old age, both for epidemiologic studies and in clinical practice. The adaptation of dementia screening for vision-impaired older persons has proved to be a successful way of obtaining valid results of cognitive functioning. Our results have the following implications for the adaptation of screening instruments with vision-dependent items for vision-impaired older persons in general. (1) Age- and education-specific norms for the blind version should be developed to provide a valid basis for the interpretation of the test results. (2) If it is not possible to establish norms for a blind version, the
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method of linear transformation of scores on the blind version can be applied to estimate the scores for the full test version. However, estimated scores should be interpreted with caution because they may over- or underestimate cognitive functioning. To assess possible errors of estimation the item difficulties of the original and blind versions can be compared. An “easier” or “more difficult” blind version than the original test version would result in over- or underestimation of test performance. Acknowledgments This article was supported by the German Bundesministerium für Bildung und Forschung (BMBF), Interdisciplinary Centre for Clinical Research (IZKF) at the University of Leipzig (01KS9504, Projekt C7 79934700). We would also like to thank the anonymous reviewers for their helpul comments on earlier drafts.
References [1] Launer LJ, Dinkgreve MA, Jonker C, Hooijer C, Lindeboom J. Are age and education independent correlates of the Mini-Mental State Exam performance of community-dwelling elderly? J Gerontol 1993; 48(6):271–7. [2] Reischies FM, Geiselmann B. Age-related cognitive decline and vision impairment affecting the detection of dementia syndrome in old age. Br J Psychiatry 1997;171:449–51. [3] Jagger C, Clarke M, Anderson J, Battcock T. Misclassification of dementia by the Mini-Mental State Examination—are education and social class the only factors? Age Ageing 1992;21:404–11. [4] Cosi V, Citterio A, Ratti MT, Romani A. Pavia memory project: study design and first results. Ital J Neurol Sci 1995;16:141–8. [5] Korten AE, Henderson AS, Christensen H, Jorm AF, Rodgers B, Jacomb P, Mackinnon AJ. A prospective study of cognitive function in the elderly. Psychol Med 1997;27:919–30. [6] Riedel-Heller SG, Busse A, Angermeyer MC. Are cognitively impaired individuals adequately represented in community surveys? Recruitment challenges and strategies to facilitate participation in community surveys of older adults. A review. Eur J Epidemiol 2000;16:827–35. [7] Uhlmann RF, Larson EB, Koepsell TD, Rees TS, Duckert LG. Visual impairment and cognitive dysfunction in Alzheimer’s disease. J Gen Intern Med 1991;6(2):126–32. [8] Fichter MM, Meller I, Schroeppel H, Steinkirchner R. Dementia and cognitive impairment in the oldest old in the community. Prevalence and comorbidity. Br J Psychiatry 1995;166:621–9.
915
[9] Riedel-Heller SG, Schork A, Matschinger H, Angermeyer MC. Recruitment procedures and their impact on the prevalence of dementia: results from the Leipzig Longitudinal Study of the Aged (LEILA75). Neuroepidemiology 2000;19:130–40. [10] Klaver CC, Wolfs RC, Vingerling JR, Hofman A, de Jong PT. Agespecific prevalence and causes of blindness and visual impairment in an older population: the Rotterdam Study. Arch Ophthalmol 1998; 116:653–8. [11] Hirvela H, Laatikainen L. Visual acuity in a population aged 70 years or older; prevalence and causes of visual impairment. Acta Ophthalmol Scand 1995;73(2):99–104. [12] Tielsch JM, Sommer A, Witt K, Katz J, Royall RM. The Baltimore Eye Survey Research Group. Blindness and visual impairment in an American urban population: The Baltimore Eye Survey. Arch Ophthalmol 1990;108:286–90. [13] Radloff LS. The CES-D Scale: a selfrReport depression scale for research in the general population. Appl Psychol Measure 1977;1(3):385–401. [14] Zaudig M, Mittelhammer J, Hiller W. SIDAM- Strukturiertes Interview für die Diagnose der Demenz vom Alzheimer Typ, der Multiinfarkt-Demenz und Demenzen anderer Ätiologie nach DSM-III-R und ICD-10-Manual. München: Logomed; 1990. [15] Zaudig M, Mittelhammer J, Hiller W, Pauls A, Thora C, Morinigo A, Mombour W. SIDAM: a structured interview for the diagnosis of dementia of the Alzheimer type, multi-infarct dementia and dementias of other aetiology according to ICD-10 and DSM-III-R. Psychol Med 1991;21:225–36. [16] Zaudig M. A new systematic method of measurement and diagnosis of “mild cognitive impairment” and dementia according to ICD-10 and DSM-III-R criteria. Int Psychogeriatr 1992;4(2):203–19. [17] Folstein MF, Folstein SE, McHugh PR. Mini-Mental-State: a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 1975;12:189–98. [18] American Psychiatric Association. Diagnostic and statistical manual of mental disorders DSM-IV. 4th ed. Washington, DC: APA; 1994. [19] Pasquier F. Early diagnosis of dementia: neuropsychology. J Neurol 1999;246:6–15. [20] Collie A, Maruff P. The neuropsychology of pre-clinical Alzheimer’s disease and mild cognitive impairment. Neurosci Biobehav Rev 2000;24:365–74. [21] Commenges D, Gagnon M, Letenneur L, Dartigues JF, BarbergerGateau P, Salamon R. Improving screening for dementia in the elderly using Mini-Mental State Examination subscores, Benton’s Visual Retention Test, and Isaacs’ Set Test. Epidemiology 1992;3(2):185–8. [22] Fabrigoule C, Rouch I, Taberly A, Letenneur L, Commenges D, Mazaux JM, Orgogozo JM, Dartigues JF. Cognitive process in preclinical phase of dementia. Brain 1998;121:135–41. [23] Masur DM, Sliwinski M, Lipton RB, Blau AD, Crystal HA. Neuropsychological prediction of dementia and the absence of dementia in healthy elderly persons. Neurology 1994;44:1427–32. [24] Tombaugh TN, McIntyre NJ. The Mini-Mental State Examination: a comprehensive review. J Am Geriatr Soc 1992;40:922–35.