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A scale for assessing quality of life in adult asthma sufferers
Journal of Psychosomati~ Research, Vol. 35. No. 1, pp. 9%110. 1991. Printed in Great Britain.
0022-3999/91 $3.00 + .00 (t5 1991 Pergamon Press plc
A SCALE FOR ASSESSING QUALITY OF LIFE IN A D U L T ASTHMA SUFFERERS MICHAEL E. HYLAND, SARAH FINNIS a n d S. H. IRVINE (Received 22 February 1990; accepted in revisedform 17 July 1990) Abstract--The Asthma Questionnaire is a 68-item quality of life scale designed to be sensitive to quality of life changes in clinical trials. The questionnaire covers 11 domains of life experience, the initial domain and item sets being derived from six qualitative focus groups of asthma patients. Psychometric analysis of responses of I01 asthma patients to the initial 10l-item set showed the scale to be unidimensional despite being multi-domain, and the finding of unidimensionality was replicated during the further three stages of item refinement using 783 patients. The scale compensates for acquiescence bias as well as allowing a 'not applicable' response category. Validity of the scale was demonstrated by confirmation of expected group differences and the retest reliability was 0.948. INTRODUCTION IN RECENT years the concept o f quality o f life a n d the practice o f quality o f life assessment have b e c o m e increasingly i m p o r t a n t in medicine. Q u a l i t y o f life scales are designed to achieve one o f two objectives, an e c o n o m i c a n d a medical objective. Q u a l i t y o f life scales can be used by resource a l l o c a t o r s to aid e c o n o m i c p l a n n i n g for different g r o u p s o f patients. G i v e n finite resources, health m a n a g e r s l o o k for a w a y for assessing the benefit o f a unit cost o f t r e a t m e n t to the quality o f life o f patients. This e c o n o m i c objective is associated p a r t i c u l a r l y with the concept o f Q u a l i t y A d j u s t e d Life Years ( Q A L Y S ) a n d scales designed to m e a s u r e Q A L Y S [1]. By c o n t r a s t , m e d i c a l researchers have a clinical objective when e v a l u a t i n g types o f t r e a t m e n t in terms o f the overall benefit to an i n d i v i d u a l p a t i e n t or to a type o f patient. Q u a l i t y o f life scales [2] are one o f a variety o f measures, including m o r t a l i t y a n d m o r b i d i t y , which can be used to assess the o u t c o m e o f clinical interventions. A s t h m a is a c h r o n i c disease o f variable but reversible airways o b s t r u c t i o n which has significant effects on the life style o f sufferers. M a n a g e m e n t o f a s t h m a includes b o t h b e h a v i o u r a l a n d p h a r m a c e u t i c a l aspects, a n d it is therefore useful to have a scale t h a n can e v a l u a t e the effect on life style o f different b e h a v i o u r a l o r p h a r m a c e u tical t r e a t m e n t p r o g r a m s . The Living with A s t h m a Q u e s t i o n n a i r e presented in this p a p e r is designed to satisfy the medical objective. The i n t e n t i o n is to p r o v i d e a quality o f life scale which can be used by researchers to evaluate the effectiveness o f t r e a t m e n t m a n a g e m e n t p r o g r a m s for a d u l t a s t h m a sufferers. EXISTING SCALES RELEVANT TO QUALITY OF LIFE ASSESSMENT FOR ASTHMATICS I f a quality o f life scale is to be used for t r e a t m e n t evaluation, a m a j o r objective is that it should be sensitive to changes in quality o f life. Q u a l i t y o f life can be assessed either t h r o u g h a disease specific (i.e. a s t h m a specific) scale, o r t h r o u g h a general scale, Requests for reprints should be sent to: Dr Michael Hyland, Department of Psychology, Polytechnic South West, Plymouth PL8 4AA, Devon, U.K. 99
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such as the Sickness Impact Profile [3, 4] or Nottingham Health Profile [5]. The major advantage of an asthma specific scale is that the exclusivity of the items to asthma will enhance sensitivity of the scale as variance from items irrelevant to asthma experience is eliminated. There are several disease-specific scales which are relevant to quality of life assessment in asthma sufferers and which could be used for that purpose. The Asthma Symptom Checklist (ASC) [6, 7] consists of 36 symptoms which can occur in connection with asthma attacks. The symptoms some of which are mood (e.g. worried, frightened) and some somatic (e.g. hard to breathe, coughing) were selected from an original set of items based on patient interviews. Psychometric analysis [6] has shown the scale to be multidimensional, the factors being panic-fear, irritability, hyperventilation hypnocapnia, broncoconstriction, and fatigue, and the factor structure has been replicated [8]. The p a n i ~ f e a r dimension is of particular interest because it is unrelated to pulmonary function but is related to steroid prescribing [7] and physicians' judgements of severity [8]. Because the scale is a symptom checklist rather than a quality of life scale, experiences relating to activities of living are not included. Furthermore, the scale is written to assess asthma attacks rather than the period between the attacks. Nevertheless, the scale has stable psychometric properties that can be employed to measure a restricted range of experiences characterizing asthma sufferers. The Guyatt scale [9, 10] was designed to measure quality of life in patients with chronic airflow limitation. The 108-item interviewer administered scale was developed using a mixed patient population all of whom demonstrated airflow limitation but only some of whom were asthmatic (i.e. demonstrated reversibility). Items include both dysphoric states (e.g. angry, discouraged) and activities (e.g. having to avoid smoky rooms, walking uphill). The researchers identified a number of domains where chronic airflow limitation affected quality of life, but did not examine the statistical relationship between those domains or related psychometric properties of the scale. The domains and associated items were based on a variety of sources, including unstructured interviews with patients and health professionals evaluation. A useful finding was that there was only a limited relationship between pulmonary function and quality of life. The Guyatt scale provides an interesting insight into quality of life for chronic airflow limitation patients but has some disadvantages as an assessment tool for asthma sufferers. First, the scale was not designed specifically for asthma sufferers and so has not been designed for maximum sensitivity in terms of the criteria of inclusivity and exclusivity. Second, the psychometric properties of the scale require more detailed investigation. The Attitudes to Asthma Scale [11, 12] consists of '31 statements regarding attitudes and beliefs thought to be important in determining illness behaviour in asthma' ([11], p. 98). By implication, the item set is physician determined. Sibbald reports a three-factor solution from the scale, the factors being respectively, 'stigma', 'confidence in doctor', and 'self-confidence in self care'. No eigenvalues (used to judge the number of factors to be extracted) or factor loadings are reported to support this three-factor extraction. A recent analysis of responses of 300 subjects who completed the Attitudes to Asthma Scale (Jones, pers. commun. January 1990) failed to replicate the three-factor solution. Jones reports an alternative two-factor solution, 'anxiety about asthma' and 'confidence in the doctor'. The Attitudes to Asthma Scale
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has uncertain psychometric properties. Although the items are designed to be exclusive to asthma sufferers, the range of items is limited by the derivation of the items from a source other than patients. In particular, items relating to activities are not included. U N D E R L Y I N G R A T I O N A L E F O R T H E LIVING W I T H A S T H M A Q U E S T I O N N A I R E
The formulation of the Living with Asthma Questionnaire was based on the following methodological considerations. 1. Derivation of original item set The eventual form of a questionnaire is considerably influenced by the original item set. According to the present interpretation, 'quality of life' refers to the patient's own subjective interpretation of their life rather than an 'objective' assessment by a physician of the patient's life. Using this interpretation of quality of life, it is clear that patients' freely elicited responses should be used as the basis for formulating the first set of items as patients and health professionals can have different understandings of the patient's illness [13]. 2. Designing for sensitivity There are two major factors which affect the sensitivity of a scale. The first is the relationship between the items in the scale and the disease. Items should be selected on the basis of exclusivity (only items relevant to the condition) and inclusivity (all items relevant to the condition) to maximize the effect of asthma experience on the scale scores. The second factor is the mode of response. With regard to a self-administered questionnaire, binary category responses (e.g. 'true' vs 'untrue') tend to be less sensitive than multi-category responses (e.g. 'very true', 'slightly true', 'untrue'). The optimum number of categories in a multi-category format should reflect the discriminability of the item and usually this is between three and seven categories. 3. Multi-domain vs multi-dimensional scales Quality of life is multi-domain in that a particular condition may affect life experiences in a variety of ways. For example, one domain may relate to emotional experience, another to sporting activities. A scale has more than one dimension if it consists of groups of statistically related items where the groups are statistically independent of each other. In a multi-domain scale, each of the domains may or may not relate to a different dimension in the scale, but whether or not this happens is an empirical question. There is no logical relationship between domains and dimensions: only an empirical relation. 4. Rel~'nement of the scale A scale should be refined (i.e. items changed or deleted) through repeated application to different populations. In particular, in multi-dimensional scales refinement often has the objective of ensuring separation (i.e. noncorrelation) of the different dimensions.
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5. Acquiescence bias
Acquiescence bias is the tendency to agree with items irrespective of the content of the item. If quality of life questionnaires provide the patient with a list of possible negative experiences, patients will tend to endorse those items irrespective of their true experience; and this bias will be greater in some patients compared with others. The standard method for compensating for acquiescence bias in test construction is to include both negative and positive items, and the failure to do this in most quality of life scalesis a methodological weakness. 6. Self-administered vs interview .format
Interviews provide an opportunity for rewording questions which are not understood by a particular patient and there is some evidence [14] that they give a more accurate measure of symptom reporting. The development of a self-administered questionnaire is therefore more demanding in terms of item quality than an interview-based questionnaire. The Living with Asthma Questionnaire was developed using the self-administered format, but without prejudice to the eventual use of the scale as interview-based or self-administered. In summary, the development of the Living with Asthma Questionnaire is; (a) based on patients' reports; (b) is designed for sensitivity; (c) is refined through several versions of the scale; (d) treats the issue of dimensionality empirically; and (e) compensates for acquiescence bias. METHODS AND RESULTS 1. Initial item set
Interviews on a one to one basis with a health professional can be intimidating for a patient. More importantly, the context of the interview may elicit patient responses with a treatment/medical orientation. We decided to use the alternative strategy of focus groups. In a focus group, the researcher outlines the purpose of research to a group of about six to eight individuals, and the interaction between the group members provides the information with minimal intervention by the researcher. Six focus groups were held. Four of the groups were recruited through GPs at two different practices (two groups from each practice) where management of asthma was somewhat different: one of the practices ran an asthma clinic, one did not. The remaining two groups were obtained from a campus population (primarily undergraduates) through advertisements. The maximum and minimum number of people in the groups were ten and three respectively. The venue was hotels for the GP referred patients and a seminar room for the campus population. The researcher introduced each session by explaining the purpose of the research, i.e. to generate items for a questionnaire, and then asked patients to provide information about their 'everyday life experiences of living with asthma'. The one-hour sessions required little prompting, and comments from the free ranging discussions were classified in 11 domains as follows: social/leisure, sport, sleep, holidays, work and other activities, colds, mobility, effects on others, medication usage, doctors, and dysphoric states and attitudes.
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The first version of the questionnaire, AQ1 consisted of 101 items, many of which were verbatim comments from the focus groups, and which represented the 11 domains listed above. An additional domain of two items was added, namely that of sexual behaviour as it was felt that the group discussion may have inhibited talk about sexuality. Thus, AQ1 covered 12 domains, and the number of items within each of the domains reflected the degree of discussion topics received in the focus groups. Response to each of the items was on a four-point category scale which varied from 'untrue of me' to 'very true of me'. Instructions for filling in the questionnaire (including examples) were placed at the beginning of the questionnaire. Open-ended questions at the end of the questionnaire solicited 'any other issue which is important to you and is not on the questionnaire' and 'anything else relevant to the questionnaire'.
2. Results from AQ 1 and production of AQ2 The AQ1 was distributed through 18 GPs to patients who were 18 yr or more in age and where the patient was clinically diagnosed as having asthma. Either the GP gave the questionnaire to patients after an appointment, or instructed the practice manager to distribute the questionnaire to patients requiring a repeat prescription of a bronchodilator. (Note: this method of distribution does not allow calculation of return rate.) The patient completed the questionnaire at home and returned it in a F R E E P O S T envelope. 101 patients completed AQ1. A trial principal factor analysis indicated a one-factor solution using the scree test as a criterion [15]. Twoand three-factor solutions were also tried using Maximum Likelihood as the method of extraction with orthogonal (varimax) and oblique rotations, but meaningful solutions were not obtained. The first factor accounted for 26.2% of the total variance. Following conventional psychometric practice, items were deleted or modified if: (a) they were poor discriminators, i.e. 70% or more of patients endorsed one response; (b) if the factor loading on the first factor was less than 0.3; and (c) if the question was reported as problematic in the open-ended response. The open-ended question did not produce any new domains, but several patients indicated that some items were 'not applicable' rather than not true. Although there is some logical overlap between 'not true' and 'not applicable', the latter description was added to the 'not true' category (i.e. 'either not true or not applicable') for AQ2. The AQ2 consisted of 77 items.
3. Results from AQ2 and production of AQ3 One hundred and fifty patients recruited through 23 (additional) GPs completed AQ2. Trial principal factor analysis again indicated a single factor solution and where the first factor accounted for 24.8% of the total variance. There were three 'doctor' items remaining in AQ2 and as these continued to show low factor loadings with the general factor, the domain of 'doctor' items was deleted. The issue of the patient's relationship with the doctor is an important one, but it seems to be relatively independent of the general factor. For other items, item modification and rejection were carried out using the previous criteria of low item variability, low factor loadings and informal patient comment. In addition, the polarity of some items was changed to increase the number of positive items (e.g. 'asthma makes no difference
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to my life'). Because AQ1 items were based primarily on verbatim reports from the focus groups, the number of positive items was low. The AQ2 consisted of 49 negative items and 28 positive items. The AQ3 consisted of 43 negative items and 29 positive items. It was found to be comparatively difficult to find positive items without introducing negatives into the item (negatives are known to lead to comprehension difficulties which shows up in low factor loadings) and this is reflected in the lower number of positive items in the total AQ3 set.
4. Results from AQ3 and production of AQ4 Four hundred and five patients completed AQ3 of whom 225 were recruited through 78 GPs (from different regions throughout the U K ) and 180 through an advertisement placed in Asthma News, the newsletter of the Asthma Society. Factor loadings are shown in Table I. A front page of AQ3 requested demographic information and patients were asked to indicate in which of 10 regions (e.g south-west, north-east) they lived. For each subject scale scores were obtained by adding the rating ( 1 4 ) for each negative item to the ratings with reversed polarity (4-1) for the positive items. Scale scores showed no difference with regard to region, F(9,391) = 0.58, ns. Mean scale scores for Asthma Society recruits and G P recruits were 174 and 158 respectively, t ( 4 0 3 ) = 4.02, p < 0.001. Means for each item for Asthma Society and GP recruits are shown in Table I. These data suggest that there is a general trend rather than a domain specific trend for Asthma Society recruits to have a lower quality of life than the GP recruits. Four items were dropped between AQ3 and AQ4. The number of items per domain in AQ4 is shown in Table II. A new format for the response scale was used in AQ4. There was still a small minority who found the not true/not applicable category difficult to use as a combined category. Furthermore, failure to distinguish 'not applicable' from 'untrue of me' for positive items (but not negative items) can lead to an incorrect overestimate of disadvantage on that item. Patients responded to AQ4 on a three-point scale, 'untrue of me', 'slightly true of me', and 'very true of me'. In addition, subjects could respond 'not applicable'. Subjects responded by filling in circles, and to prevent confusion the 'not applicable' circle was positioned to the side and slightly below the line of circles for the other response categories. Modified instructions with a description of 'not applicable' were included at the beginning of the questionnaire and item 1 was used as exemplar of when an item might be 'not applicable', as opposed to 'untrue of me'.
5. Results from A Q 4 The AQ4 was distributed by post to 282 asthma sufferers who had taken part in the earlier studies and who had indicated that they would be prepared to participate in further research. There were 228 questionnaires returned (return rate 81%). A scree plot again indicated a unifactorial solution, the eigenvalues for the first six factors in a trial principal factor analysis being 20.2, 4.0, 2.5, 2.3, 2.0, 1.7. The first factor accounted for 29.8% of the total variance, and the increased accounted variance of the first factor between AQ3 and AQ4 is probably attributable to the new response format.
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M . E . I-]YLAND et al. TABLE II.--NUMBER OF NEGATIVEAND POSITIVE ITEMSIN EACH OF 11 DOMAINS IN THE LIVING WITH ASTHMA QUESTIONNAIRE N u m b e r of Q u e s t i o n s Negative Positive
Domains Social/leisure Sport Holidays Sleep W o r k a n d other activities Colds Mobility Effects on others M e d i c a t i o n usage Sex D y s p h o r i c states a n d attitudes Totals
5 2 1 3 4 4 3 3 5 I
1 1 2 1 2 1 3 2 1 0
13 44
10 24
Table I provides the following information for AQ4: factor loadings for all subjects, factor loadings for males and females, means for males and females, item distribution. There is a tendency for factor loadings for the female subjects to be slightly lower than those of the males (a similar pattern emerged from the AQ3 data), though this is difficult to interpret. The age distribution of the sample is shown in Table III. For each subject, scale scores for AQ4 were calculated by adding the values of each negative item (1 3) to the values of each positive item reversed in polarity (3 1) and dividing by the number of positive and negative items. This method of calculating scale scores compensates for patients having different numbers of 'not applicable' responses. Mean scale scores for 102 males and 124 females are 1.89 and 2.00 respectively, t(224)= 1.96, p = 0.05. The difference between males and females is only just significant at the 0.05 level; although statistical significance is achieved, the size of the effect is small. Mean scale scores for different ages are shown in Table III, F(5,222) = 4.8, p < 0.001. Inspection of the means shows that quality of life decreases with age but that there is little change after the age of 35.
Reliability Questionnaires (AQ4) were sent to 81 patients who had been recruited through GPs, and had indicated their willingness for further participation. There were 136 questionnaires returned. Questionnaires were sent out again after two months and 95 were returned. Scale scores were calculated and the correlation between the test TABLE I l l . - - M E A N SCALESCORES BY AGE FROM 228 RESPONSES TO A Q 4 Age 18 25 35 45 55 66
24 34 44 54 64
N
Scale Score
29 36 26 38 43 56
1.T1 1.78 2.02 1.94 2.05 2.06
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and retest measures was r = 0.95, indicating that the scale is highly reliable, at least with that particular group of (probably highly motivated) patients. DISCUSSION The Living with Asthma Questionnaire (AQ4) is a 68-item, unidimensional, multi-domain scale designed to measure quality of life in asthma sufferers. The scale is derived from patients' freely elicited statements and includes some items not included in other asthma-relevant scales, for example, concern about going away on holiday, colds and medication usage. The scale provides some compensation for acquiescence bias, the fewer positive items (24) compared to the negative items (44) reflecting the greater difficulty of obtaining high loading positive items, particularly in the social/leisure domain. Although quality of life in asthma sufferers is multidomain, this research provides clear evidence that responses across the majority of domains are unidimensional. That is, perceived dysfunction in one domain is correlated with perceived dysfunction in other domains. Although other asthma-relevant scales [6, 9, 12] have been reported as being multidimensional, whether a scale is unidimensional or not depends on the items. Certainly the evidence suggests that a broadly based pool of items--and which are not predominantly mood items--does tend to produce a unidimensional solution. The Living with Asthma Questionnaire was designed to include a broad range of items which are characteristic only of asthma sufferers. The breadth of items is evident from a comparison with other scales. For instance, compared with the 108-item Guyatt scale, the Living with Asthma Questionnaire includes items relating to sport, holidays, colds, effects on others and medication usage. On the other hand, the Living with Asthma Questionnaire has less items on emotional experience compared with the Guyatt scale, nor does it include anything corresponding to the Guyatt category of cognitive impairment. Some validation of the scale was achieved by comparing different subgroups of patients. Patient recruitment is seldom truly random. The AQ3 data were obtained from a mixed population of Asthma Society recruits and GP recruits. It is possible that the GPs who responded to our request for help were particularly interested in asthma and that their patients are over-represented by well managed patients, that is over-represented by comparison with the Asthma Society recruits. If good management contributes to improved quality of life, Asthma Society recruits should have a lower quality of life than GP recruits. This was found to be the case. Evidently, the Living with Asthma Questionnaire is sensitive to differences which one might expect from two differently recruited groups of patients. The scale shows that there are sex differences, though these are small, and that there are also age differences in quality of life. The decrease in quality of life with increasing age is intuitively to be expected. The slightly lower quality of life in males compared with females is difficult to interpret though this effect seems to be general rather than domain specific (see Table I). In general, the Living with Asthma Questionnaire appears to be sensitive to group differences based on age, sex and patient recruitment. The retest reliability of the scale is particularly high, though it could be argued that the reliability data were obtained on self-selected subjects who may have had above
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average questionnaire completion skills. Although the questionnaire was developed in a self-administered rather than interviewer-administered format, there seems to be no reason to preclude the use of the scale in an interviewer format which might improve accuracy of reporting in some cases. We have found the interviewer format to take at most 15-20 rain. Acknowledgements--Thanks are due to the General Practitioners who distributed questionnaires to their patients and to the patients for filling in the questionnaire. We also thank the A s t h m a Society who helped recruitment of patients through Asthma News and Allen & Hanburys for financial support.
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TORRANCEGW, Measurement of health state utilities for economic appraisal. J Health Econ 1986; 5 : 1 30. KAPLAN RM. Health-related quality of life in cardiovascular disease. J Consult Clin Psychol 1988: 56: 382-392. BERGER, M, BOBBWr RA, KRESSEL S, POLLARD WE, GILSON BS, MORRIS JR. The Sickness Impact Profile: conceptual formulation and methodology for the development of a health status measure. lnt J Health Serv 1976; 6: 393~15. BERGERM, BOBBITTRA, CARTERW, G1LSON BS. The Sickness Impact Profile: development and final revision of a health status measure. Med Care 1981; 19: 787-805. I-tUNTSJ, McEwAN J, McKENNA SP. Measuring Health Status. London: Croom Helm, 1986. KINSMAN RA, LUr'ARELLOT, O'BAN1ON K, SPECTOrt S. Multidimensional analysis of the subjective symptomatology of asthma. Psychosom M e d 1973; 35:250 267. KINSMANRA, DAHLEMN W , SPECTORS, STAUDENMAYERH. Observations on subjective symptomatology, coping behavior, and medical decisions in asthma. Psychosom Med 1977; 39:102 119. BROOKSCM, RICrtARDS JM, BAILEYWC, MARTIN B, WINDSOR RA, SOONG S-J. Subjective symptomatology of asthma in an outpatient population. Psychosom Med 1989; 51:102 108. GUYATT GH, BERMANLB, TOWNSEND M, PUGSLEY SO, CHAMBERSLW. A measure of quality of life for clinical trials in chronic lung disease. Thorax 1987; 42:773 778. Gt;VATT GH, TOWYSENDM, BERMANLB, Pt:GSLEY SO. Quality of life in patients with chronic airflow limitation. Br J Dis Chest 1987; 8 1 : 4 5 54. SIBBALD B. Patient self care in acute asthma. Thorax 1989; 4 4 : 9 7 101. SIBBALD B, WHITE P, PHAROAHC, FREELING P, ANDERSON HR. Relationship between psychosocial factors and asthma morbidity. Fam Practice 1988; 5 : 1 2 17. DIRKS JF, HORTON DJ, KINSMAN RA, FROSS K H , JONES NF. Patient and physician characteristics influencing medical decisions in asthma. J Asthma Res 1978; 15:171 178. ANDERSON JP, BUSH JW, BERRY CC. Internal consistency analysis: A method for studying the accuracy of function assessment for health outcome and quality of life evaluation. J Clin Epidemiol 1988; 41:127 137. CATTEI.LRB. Factor Analysis. New York: Harper, 1952.
0022-3999/91 $3.00 + .00 (t5 1991 Pergamon Press plc
A SCALE FOR ASSESSING QUALITY OF LIFE IN A D U L T ASTHMA SUFFERERS MICHAEL E. HYLAND, SARAH FINNIS a n d S. H. IRVINE (Received 22 February 1990; accepted in revisedform 17 July 1990) Abstract--The Asthma Questionnaire is a 68-item quality of life scale designed to be sensitive to quality of life changes in clinical trials. The questionnaire covers 11 domains of life experience, the initial domain and item sets being derived from six qualitative focus groups of asthma patients. Psychometric analysis of responses of I01 asthma patients to the initial 10l-item set showed the scale to be unidimensional despite being multi-domain, and the finding of unidimensionality was replicated during the further three stages of item refinement using 783 patients. The scale compensates for acquiescence bias as well as allowing a 'not applicable' response category. Validity of the scale was demonstrated by confirmation of expected group differences and the retest reliability was 0.948. INTRODUCTION IN RECENT years the concept o f quality o f life a n d the practice o f quality o f life assessment have b e c o m e increasingly i m p o r t a n t in medicine. Q u a l i t y o f life scales are designed to achieve one o f two objectives, an e c o n o m i c a n d a medical objective. Q u a l i t y o f life scales can be used by resource a l l o c a t o r s to aid e c o n o m i c p l a n n i n g for different g r o u p s o f patients. G i v e n finite resources, health m a n a g e r s l o o k for a w a y for assessing the benefit o f a unit cost o f t r e a t m e n t to the quality o f life o f patients. This e c o n o m i c objective is associated p a r t i c u l a r l y with the concept o f Q u a l i t y A d j u s t e d Life Years ( Q A L Y S ) a n d scales designed to m e a s u r e Q A L Y S [1]. By c o n t r a s t , m e d i c a l researchers have a clinical objective when e v a l u a t i n g types o f t r e a t m e n t in terms o f the overall benefit to an i n d i v i d u a l p a t i e n t or to a type o f patient. Q u a l i t y o f life scales [2] are one o f a variety o f measures, including m o r t a l i t y a n d m o r b i d i t y , which can be used to assess the o u t c o m e o f clinical interventions. A s t h m a is a c h r o n i c disease o f variable but reversible airways o b s t r u c t i o n which has significant effects on the life style o f sufferers. M a n a g e m e n t o f a s t h m a includes b o t h b e h a v i o u r a l a n d p h a r m a c e u t i c a l aspects, a n d it is therefore useful to have a scale t h a n can e v a l u a t e the effect on life style o f different b e h a v i o u r a l o r p h a r m a c e u tical t r e a t m e n t p r o g r a m s . The Living with A s t h m a Q u e s t i o n n a i r e presented in this p a p e r is designed to satisfy the medical objective. The i n t e n t i o n is to p r o v i d e a quality o f life scale which can be used by researchers to evaluate the effectiveness o f t r e a t m e n t m a n a g e m e n t p r o g r a m s for a d u l t a s t h m a sufferers. EXISTING SCALES RELEVANT TO QUALITY OF LIFE ASSESSMENT FOR ASTHMATICS I f a quality o f life scale is to be used for t r e a t m e n t evaluation, a m a j o r objective is that it should be sensitive to changes in quality o f life. Q u a l i t y o f life can be assessed either t h r o u g h a disease specific (i.e. a s t h m a specific) scale, o r t h r o u g h a general scale, Requests for reprints should be sent to: Dr Michael Hyland, Department of Psychology, Polytechnic South West, Plymouth PL8 4AA, Devon, U.K. 99
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such as the Sickness Impact Profile [3, 4] or Nottingham Health Profile [5]. The major advantage of an asthma specific scale is that the exclusivity of the items to asthma will enhance sensitivity of the scale as variance from items irrelevant to asthma experience is eliminated. There are several disease-specific scales which are relevant to quality of life assessment in asthma sufferers and which could be used for that purpose. The Asthma Symptom Checklist (ASC) [6, 7] consists of 36 symptoms which can occur in connection with asthma attacks. The symptoms some of which are mood (e.g. worried, frightened) and some somatic (e.g. hard to breathe, coughing) were selected from an original set of items based on patient interviews. Psychometric analysis [6] has shown the scale to be multidimensional, the factors being panic-fear, irritability, hyperventilation hypnocapnia, broncoconstriction, and fatigue, and the factor structure has been replicated [8]. The p a n i ~ f e a r dimension is of particular interest because it is unrelated to pulmonary function but is related to steroid prescribing [7] and physicians' judgements of severity [8]. Because the scale is a symptom checklist rather than a quality of life scale, experiences relating to activities of living are not included. Furthermore, the scale is written to assess asthma attacks rather than the period between the attacks. Nevertheless, the scale has stable psychometric properties that can be employed to measure a restricted range of experiences characterizing asthma sufferers. The Guyatt scale [9, 10] was designed to measure quality of life in patients with chronic airflow limitation. The 108-item interviewer administered scale was developed using a mixed patient population all of whom demonstrated airflow limitation but only some of whom were asthmatic (i.e. demonstrated reversibility). Items include both dysphoric states (e.g. angry, discouraged) and activities (e.g. having to avoid smoky rooms, walking uphill). The researchers identified a number of domains where chronic airflow limitation affected quality of life, but did not examine the statistical relationship between those domains or related psychometric properties of the scale. The domains and associated items were based on a variety of sources, including unstructured interviews with patients and health professionals evaluation. A useful finding was that there was only a limited relationship between pulmonary function and quality of life. The Guyatt scale provides an interesting insight into quality of life for chronic airflow limitation patients but has some disadvantages as an assessment tool for asthma sufferers. First, the scale was not designed specifically for asthma sufferers and so has not been designed for maximum sensitivity in terms of the criteria of inclusivity and exclusivity. Second, the psychometric properties of the scale require more detailed investigation. The Attitudes to Asthma Scale [11, 12] consists of '31 statements regarding attitudes and beliefs thought to be important in determining illness behaviour in asthma' ([11], p. 98). By implication, the item set is physician determined. Sibbald reports a three-factor solution from the scale, the factors being respectively, 'stigma', 'confidence in doctor', and 'self-confidence in self care'. No eigenvalues (used to judge the number of factors to be extracted) or factor loadings are reported to support this three-factor extraction. A recent analysis of responses of 300 subjects who completed the Attitudes to Asthma Scale (Jones, pers. commun. January 1990) failed to replicate the three-factor solution. Jones reports an alternative two-factor solution, 'anxiety about asthma' and 'confidence in the doctor'. The Attitudes to Asthma Scale
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has uncertain psychometric properties. Although the items are designed to be exclusive to asthma sufferers, the range of items is limited by the derivation of the items from a source other than patients. In particular, items relating to activities are not included. U N D E R L Y I N G R A T I O N A L E F O R T H E LIVING W I T H A S T H M A Q U E S T I O N N A I R E
The formulation of the Living with Asthma Questionnaire was based on the following methodological considerations. 1. Derivation of original item set The eventual form of a questionnaire is considerably influenced by the original item set. According to the present interpretation, 'quality of life' refers to the patient's own subjective interpretation of their life rather than an 'objective' assessment by a physician of the patient's life. Using this interpretation of quality of life, it is clear that patients' freely elicited responses should be used as the basis for formulating the first set of items as patients and health professionals can have different understandings of the patient's illness [13]. 2. Designing for sensitivity There are two major factors which affect the sensitivity of a scale. The first is the relationship between the items in the scale and the disease. Items should be selected on the basis of exclusivity (only items relevant to the condition) and inclusivity (all items relevant to the condition) to maximize the effect of asthma experience on the scale scores. The second factor is the mode of response. With regard to a self-administered questionnaire, binary category responses (e.g. 'true' vs 'untrue') tend to be less sensitive than multi-category responses (e.g. 'very true', 'slightly true', 'untrue'). The optimum number of categories in a multi-category format should reflect the discriminability of the item and usually this is between three and seven categories. 3. Multi-domain vs multi-dimensional scales Quality of life is multi-domain in that a particular condition may affect life experiences in a variety of ways. For example, one domain may relate to emotional experience, another to sporting activities. A scale has more than one dimension if it consists of groups of statistically related items where the groups are statistically independent of each other. In a multi-domain scale, each of the domains may or may not relate to a different dimension in the scale, but whether or not this happens is an empirical question. There is no logical relationship between domains and dimensions: only an empirical relation. 4. Rel~'nement of the scale A scale should be refined (i.e. items changed or deleted) through repeated application to different populations. In particular, in multi-dimensional scales refinement often has the objective of ensuring separation (i.e. noncorrelation) of the different dimensions.
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5. Acquiescence bias
Acquiescence bias is the tendency to agree with items irrespective of the content of the item. If quality of life questionnaires provide the patient with a list of possible negative experiences, patients will tend to endorse those items irrespective of their true experience; and this bias will be greater in some patients compared with others. The standard method for compensating for acquiescence bias in test construction is to include both negative and positive items, and the failure to do this in most quality of life scalesis a methodological weakness. 6. Self-administered vs interview .format
Interviews provide an opportunity for rewording questions which are not understood by a particular patient and there is some evidence [14] that they give a more accurate measure of symptom reporting. The development of a self-administered questionnaire is therefore more demanding in terms of item quality than an interview-based questionnaire. The Living with Asthma Questionnaire was developed using the self-administered format, but without prejudice to the eventual use of the scale as interview-based or self-administered. In summary, the development of the Living with Asthma Questionnaire is; (a) based on patients' reports; (b) is designed for sensitivity; (c) is refined through several versions of the scale; (d) treats the issue of dimensionality empirically; and (e) compensates for acquiescence bias. METHODS AND RESULTS 1. Initial item set
Interviews on a one to one basis with a health professional can be intimidating for a patient. More importantly, the context of the interview may elicit patient responses with a treatment/medical orientation. We decided to use the alternative strategy of focus groups. In a focus group, the researcher outlines the purpose of research to a group of about six to eight individuals, and the interaction between the group members provides the information with minimal intervention by the researcher. Six focus groups were held. Four of the groups were recruited through GPs at two different practices (two groups from each practice) where management of asthma was somewhat different: one of the practices ran an asthma clinic, one did not. The remaining two groups were obtained from a campus population (primarily undergraduates) through advertisements. The maximum and minimum number of people in the groups were ten and three respectively. The venue was hotels for the GP referred patients and a seminar room for the campus population. The researcher introduced each session by explaining the purpose of the research, i.e. to generate items for a questionnaire, and then asked patients to provide information about their 'everyday life experiences of living with asthma'. The one-hour sessions required little prompting, and comments from the free ranging discussions were classified in 11 domains as follows: social/leisure, sport, sleep, holidays, work and other activities, colds, mobility, effects on others, medication usage, doctors, and dysphoric states and attitudes.
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The first version of the questionnaire, AQ1 consisted of 101 items, many of which were verbatim comments from the focus groups, and which represented the 11 domains listed above. An additional domain of two items was added, namely that of sexual behaviour as it was felt that the group discussion may have inhibited talk about sexuality. Thus, AQ1 covered 12 domains, and the number of items within each of the domains reflected the degree of discussion topics received in the focus groups. Response to each of the items was on a four-point category scale which varied from 'untrue of me' to 'very true of me'. Instructions for filling in the questionnaire (including examples) were placed at the beginning of the questionnaire. Open-ended questions at the end of the questionnaire solicited 'any other issue which is important to you and is not on the questionnaire' and 'anything else relevant to the questionnaire'.
2. Results from AQ 1 and production of AQ2 The AQ1 was distributed through 18 GPs to patients who were 18 yr or more in age and where the patient was clinically diagnosed as having asthma. Either the GP gave the questionnaire to patients after an appointment, or instructed the practice manager to distribute the questionnaire to patients requiring a repeat prescription of a bronchodilator. (Note: this method of distribution does not allow calculation of return rate.) The patient completed the questionnaire at home and returned it in a F R E E P O S T envelope. 101 patients completed AQ1. A trial principal factor analysis indicated a one-factor solution using the scree test as a criterion [15]. Twoand three-factor solutions were also tried using Maximum Likelihood as the method of extraction with orthogonal (varimax) and oblique rotations, but meaningful solutions were not obtained. The first factor accounted for 26.2% of the total variance. Following conventional psychometric practice, items were deleted or modified if: (a) they were poor discriminators, i.e. 70% or more of patients endorsed one response; (b) if the factor loading on the first factor was less than 0.3; and (c) if the question was reported as problematic in the open-ended response. The open-ended question did not produce any new domains, but several patients indicated that some items were 'not applicable' rather than not true. Although there is some logical overlap between 'not true' and 'not applicable', the latter description was added to the 'not true' category (i.e. 'either not true or not applicable') for AQ2. The AQ2 consisted of 77 items.
3. Results from AQ2 and production of AQ3 One hundred and fifty patients recruited through 23 (additional) GPs completed AQ2. Trial principal factor analysis again indicated a single factor solution and where the first factor accounted for 24.8% of the total variance. There were three 'doctor' items remaining in AQ2 and as these continued to show low factor loadings with the general factor, the domain of 'doctor' items was deleted. The issue of the patient's relationship with the doctor is an important one, but it seems to be relatively independent of the general factor. For other items, item modification and rejection were carried out using the previous criteria of low item variability, low factor loadings and informal patient comment. In addition, the polarity of some items was changed to increase the number of positive items (e.g. 'asthma makes no difference
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to my life'). Because AQ1 items were based primarily on verbatim reports from the focus groups, the number of positive items was low. The AQ2 consisted of 49 negative items and 28 positive items. The AQ3 consisted of 43 negative items and 29 positive items. It was found to be comparatively difficult to find positive items without introducing negatives into the item (negatives are known to lead to comprehension difficulties which shows up in low factor loadings) and this is reflected in the lower number of positive items in the total AQ3 set.
4. Results from AQ3 and production of AQ4 Four hundred and five patients completed AQ3 of whom 225 were recruited through 78 GPs (from different regions throughout the U K ) and 180 through an advertisement placed in Asthma News, the newsletter of the Asthma Society. Factor loadings are shown in Table I. A front page of AQ3 requested demographic information and patients were asked to indicate in which of 10 regions (e.g south-west, north-east) they lived. For each subject scale scores were obtained by adding the rating ( 1 4 ) for each negative item to the ratings with reversed polarity (4-1) for the positive items. Scale scores showed no difference with regard to region, F(9,391) = 0.58, ns. Mean scale scores for Asthma Society recruits and G P recruits were 174 and 158 respectively, t ( 4 0 3 ) = 4.02, p < 0.001. Means for each item for Asthma Society and GP recruits are shown in Table I. These data suggest that there is a general trend rather than a domain specific trend for Asthma Society recruits to have a lower quality of life than the GP recruits. Four items were dropped between AQ3 and AQ4. The number of items per domain in AQ4 is shown in Table II. A new format for the response scale was used in AQ4. There was still a small minority who found the not true/not applicable category difficult to use as a combined category. Furthermore, failure to distinguish 'not applicable' from 'untrue of me' for positive items (but not negative items) can lead to an incorrect overestimate of disadvantage on that item. Patients responded to AQ4 on a three-point scale, 'untrue of me', 'slightly true of me', and 'very true of me'. In addition, subjects could respond 'not applicable'. Subjects responded by filling in circles, and to prevent confusion the 'not applicable' circle was positioned to the side and slightly below the line of circles for the other response categories. Modified instructions with a description of 'not applicable' were included at the beginning of the questionnaire and item 1 was used as exemplar of when an item might be 'not applicable', as opposed to 'untrue of me'.
5. Results from A Q 4 The AQ4 was distributed by post to 282 asthma sufferers who had taken part in the earlier studies and who had indicated that they would be prepared to participate in further research. There were 228 questionnaires returned (return rate 81%). A scree plot again indicated a unifactorial solution, the eigenvalues for the first six factors in a trial principal factor analysis being 20.2, 4.0, 2.5, 2.3, 2.0, 1.7. The first factor accounted for 29.8% of the total variance, and the increased accounted variance of the first factor between AQ3 and AQ4 is probably attributable to the new response format.
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M . E . I-]YLAND et al. TABLE II.--NUMBER OF NEGATIVEAND POSITIVE ITEMSIN EACH OF 11 DOMAINS IN THE LIVING WITH ASTHMA QUESTIONNAIRE N u m b e r of Q u e s t i o n s Negative Positive
Domains Social/leisure Sport Holidays Sleep W o r k a n d other activities Colds Mobility Effects on others M e d i c a t i o n usage Sex D y s p h o r i c states a n d attitudes Totals
5 2 1 3 4 4 3 3 5 I
1 1 2 1 2 1 3 2 1 0
13 44
10 24
Table I provides the following information for AQ4: factor loadings for all subjects, factor loadings for males and females, means for males and females, item distribution. There is a tendency for factor loadings for the female subjects to be slightly lower than those of the males (a similar pattern emerged from the AQ3 data), though this is difficult to interpret. The age distribution of the sample is shown in Table III. For each subject, scale scores for AQ4 were calculated by adding the values of each negative item (1 3) to the values of each positive item reversed in polarity (3 1) and dividing by the number of positive and negative items. This method of calculating scale scores compensates for patients having different numbers of 'not applicable' responses. Mean scale scores for 102 males and 124 females are 1.89 and 2.00 respectively, t(224)= 1.96, p = 0.05. The difference between males and females is only just significant at the 0.05 level; although statistical significance is achieved, the size of the effect is small. Mean scale scores for different ages are shown in Table III, F(5,222) = 4.8, p < 0.001. Inspection of the means shows that quality of life decreases with age but that there is little change after the age of 35.
Reliability Questionnaires (AQ4) were sent to 81 patients who had been recruited through GPs, and had indicated their willingness for further participation. There were 136 questionnaires returned. Questionnaires were sent out again after two months and 95 were returned. Scale scores were calculated and the correlation between the test TABLE I l l . - - M E A N SCALESCORES BY AGE FROM 228 RESPONSES TO A Q 4 Age 18 25 35 45 55 66
24 34 44 54 64
N
Scale Score
29 36 26 38 43 56
1.T1 1.78 2.02 1.94 2.05 2.06
Quality of life in asthma sufferers
I09
and retest measures was r = 0.95, indicating that the scale is highly reliable, at least with that particular group of (probably highly motivated) patients. DISCUSSION The Living with Asthma Questionnaire (AQ4) is a 68-item, unidimensional, multi-domain scale designed to measure quality of life in asthma sufferers. The scale is derived from patients' freely elicited statements and includes some items not included in other asthma-relevant scales, for example, concern about going away on holiday, colds and medication usage. The scale provides some compensation for acquiescence bias, the fewer positive items (24) compared to the negative items (44) reflecting the greater difficulty of obtaining high loading positive items, particularly in the social/leisure domain. Although quality of life in asthma sufferers is multidomain, this research provides clear evidence that responses across the majority of domains are unidimensional. That is, perceived dysfunction in one domain is correlated with perceived dysfunction in other domains. Although other asthma-relevant scales [6, 9, 12] have been reported as being multidimensional, whether a scale is unidimensional or not depends on the items. Certainly the evidence suggests that a broadly based pool of items--and which are not predominantly mood items--does tend to produce a unidimensional solution. The Living with Asthma Questionnaire was designed to include a broad range of items which are characteristic only of asthma sufferers. The breadth of items is evident from a comparison with other scales. For instance, compared with the 108-item Guyatt scale, the Living with Asthma Questionnaire includes items relating to sport, holidays, colds, effects on others and medication usage. On the other hand, the Living with Asthma Questionnaire has less items on emotional experience compared with the Guyatt scale, nor does it include anything corresponding to the Guyatt category of cognitive impairment. Some validation of the scale was achieved by comparing different subgroups of patients. Patient recruitment is seldom truly random. The AQ3 data were obtained from a mixed population of Asthma Society recruits and GP recruits. It is possible that the GPs who responded to our request for help were particularly interested in asthma and that their patients are over-represented by well managed patients, that is over-represented by comparison with the Asthma Society recruits. If good management contributes to improved quality of life, Asthma Society recruits should have a lower quality of life than GP recruits. This was found to be the case. Evidently, the Living with Asthma Questionnaire is sensitive to differences which one might expect from two differently recruited groups of patients. The scale shows that there are sex differences, though these are small, and that there are also age differences in quality of life. The decrease in quality of life with increasing age is intuitively to be expected. The slightly lower quality of life in males compared with females is difficult to interpret though this effect seems to be general rather than domain specific (see Table I). In general, the Living with Asthma Questionnaire appears to be sensitive to group differences based on age, sex and patient recruitment. The retest reliability of the scale is particularly high, though it could be argued that the reliability data were obtained on self-selected subjects who may have had above
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average questionnaire completion skills. Although the questionnaire was developed in a self-administered rather than interviewer-administered format, there seems to be no reason to preclude the use of the scale in an interviewer format which might improve accuracy of reporting in some cases. We have found the interviewer format to take at most 15-20 rain. Acknowledgements--Thanks are due to the General Practitioners who distributed questionnaires to their patients and to the patients for filling in the questionnaire. We also thank the A s t h m a Society who helped recruitment of patients through Asthma News and Allen & Hanburys for financial support.
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