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Lifetime prevalence and age of onset of psychiatric disorders: Recall 4 years later
J. psychiat. Res., Vol. 22, No. 2, pp. 107-117, 1988. Printed in Great Britain.
0022-3956/88 $3.00+ .00 © 1988 Pergamon Press pie
LIFETIME P R E V A L E N C E A N D A G E OF ONSET OF P S Y C H I A T R I C DISORDERS: R E C A L L 4 Y E A R S L A T E R BRIGITTE A. PRUSOFF*, KATHLEEN R. MERIKANGAS*~ a n d MYRNA M. WEISSMAN~ *Department of Psychiatry and "~Departmentof Epidemiology, Yale University School of Medicine, Connecticut Mental Health Center, New Haven, Connecticut, U.S.A.; ~Department of Psychiatry, Collegeof Physicians and Surgeons of Columbia University, New York, New York U.S.A.
(Revised 14 July 1987) Summary--The blind test-retest reliability of lifetime prevalence and age of onset of psychiatric diagnoses, based on the SADS-Linterviewand RDC over a three-to-fiveyear period, was examined in 143 probands and their relatives. Reliability of lifetime prevalence of major depression was excellent;reliabilityof antisocialpersonality,panic disorder, drug abuse, GAD, depressivepersonality, and alcoholism was good; reliability of obsessive-compulsive disorder and phobia was acceptable but lower. The reliability of hyperthymia or cyclothymia was not acceptable. Reliability for major depression did not vary substantially by age or sex of the informant, but recall of major depression was significantly higher in the probands than in their relatives. The testretest reliability for the age of onset of major depression and panic disorder was excellent, and for phobia, GAD and alcoholism, was acceptable. Both probands and relatives recalled the age of onset of their depression fairly accurately. However, there was a reduction in agreement over time. Recall after 3-4 yr was better than 5-6 yr. There was a tendency for older respondents to systematicallyincrease the age of onset of their depression across the two interviews, although the increase was only a few years. Recall of age of onset did not differ significantlyby sex of respondent or whether the respondent was a proband or relative. These findings are discussedin light of several available studies of reliability of lifetime prevalence of psychiatric diagnoses. INTRODUCTION INFORMATION o n the lifetime prevalence o f psychiatric disorders a n d their initial onset is i m p o r t a n t b o t h in clinical practice a n d research. Since the i n t r o d u c t i o n o f s t a n d a r d i z e d psychiatric diagnostic criteria a n d structured diagnostic interviews to assess the signs a n d s y m p t o m s t h a t define the criteria, i n f o r m a t i o n o n the lifetime prevalence a n d the age o f onset o f psychiatric disorders has been o b t a i n e d with increasing frequency. T h e reliability o f assessment o f lifetime diagnosis has i m p r o v e d with the use o f these new diagnostic m e t h o d s . Several studies have assessed the test-retest reliability o f lifetime diagnosis i n patients (I~LLWR et aL, 1981; MAZtrR~ a n d GERSHON, 1979), i n relatives o f patients (ANDR~ASEN et aL, 1981; M A Z m ~ a n d GERSHON, 1979); a n d in c o m m u n i t y samples (ANDREASEN et aL, 1981; ANTI-IONYet aL, 1985; BROMET et aL, 1986; H~.LZER et al., 1985; KELLER et al., 1981; MAZtntE a n d GERSHON, 1979; Wn,rc et aL, 1977; WITTCrmN et al., 1985). I n general, these studies have f o u n d t h a t the reliability is acceptable, p a r t i c u l a r l y for alcohol dependence a n d drug abuse a n d for m a j o r depression i n patient samples (Am)R~ASEN et al., 1981; HV.LZER et aL, 1985; I~LLER et aL, 1981). Better a g r e e m e n t has b e e n observed Address reprint requests to: Brigitte A. Prusoff, Ph.D., Yale University School of Medicine, Department of Psychiatry, 350 Congress Avenue, New Haven, Connecticut, 06519, U.S.A. 107
108
BRIGITTEA. PRUSOrFet aL
among patient samples, and for those diagnoses that were elicited by experienced clinicians rather than by lay interviewers (ANDREASENet aL, 1981; KELLERet al., 1981; WITTCHEr~ et al., 1985). Most studies, with the exception of that of WITTCI-mNet aL (1985), have found that the longer the test-retest interval, the lower the reliability. There appears to be little difference in terms of reliability between the Research Diagnostic Criteria (RDC) and the American Psychiatric Association Diagnostic and Statistical Manuai-3rd Edition (DSMIII), but the reliability of the Psychiatric State Examination (PSE) (WING et al., 1977) and CATEGO (ANTHONYet al., 1985) appeared to be lower than that of the Diagnostic Interview Schedule (DIS) or the Schedule for Affective Disorders and Schizophrenia (SADS) using DSM-III or RDC. Reliability of specific symptoms has also been examined (KELr.ERet al., 1981) and found to be quite acceptable, with the exception of specific delusions and hallucinations. Increasing attention has been given to the reliability of age of onset of disorders, (ANREASENet al., 1981; BROMETet al., 1986; KELLERet al., 1981; MAZUREand GERSI-ION, 1979), since age of onset has been shown to be a predictor of longitudinal impairment and of increased familial aggregation for some disorders (WEIsSMANet al., 1984b). Accurate assignment of the age of onset of a disorder is essential to some classification schemes, such as the primary-secondary convention based on order of presentation of two disorders, and to analytic techniques that apply age-correction to the data. For example, life table analysis yields estimates of lifetime risk (LTR), which refers to the risk for onset of a particular disorder between birth and some particular age, usually the age at interview or the age at death, or the last-known age if the information is obtained from records or by report (THOMPSON and WEISSMAN, 1981). The ideal method for estimating LTR of a disorder is an unobtrusive longitudinal follow-up of persons from birth to death. Since such an approach obviously is not feasible, retrospective assessment of the life course of psychopathology is generally used to estimate lifetime prevalence. If recall of the age at which symptoms of a particular diagnosis first appeared is poor, LTR is also inaccurate. The purpose of this paper is to examine the test-retest reliability of recall of lifetime prevalence and age of onset of psychiatric disorders. The data derive from a family study of major depression in which normal and depressed probands and their first-degree relatives were reinterviewed at two points in time, approximately 4 yr apart (WEISSMANet al., 1982).
METHOD Subjects Subjects for this study were 143 probands, spouses and adult offspring who were originally part of a family-genetic study of affective disorders (WEIsSMANet al., 1982, 1984a) and were reinterviewed approximately 4 yr after their initial entrance into the study. In the original study there were 133 probands with major depression defined according to modified Research Diagnostic Criteria (requiring a 4-week duration of symptoms and impairment in the major social role). The probands had all received treatment at the Yale University Depression Research Unit or at other facilities in the Yale Department of Psychiatry. The 82 normal controls were obtained from the 1975 community survey (WEIsSMAN and MYERS, 1978) and had no history of psychiatric illness based on at least
LIFETIME PREVALENCE AND AGE OF ONSET
109
four direct interviews (the last two using SADS-RDC criteria) over an 8-yr period. All the probands were white and were grouped matched by age and sex. The original study did not include direct interviews of offspring under 18 yr of age. A direct-interview study of children was initiated 6 yr after the original study had begun, and all probands who had offspring under age 18 at the time of the original proband interview were contacted and asked to be reinterviewed. In order to determine the current and past clinical status of the parents and the older siblings of these children, the adults were interviewed separately by independent interviewers and comprise the sample for this study. The 143 subjects included 54 probands with a lifetime diagnosis of major depression, 33 normal control probands without any prior episodes of psychiatric illness, 44 of their spouses, and 12 of their offspring over age 17. The mean age of the probands and their spouses was 40 yr at the time of the initial interview and the mean age of the offspring was 19 yr; 59% of the sample were female, 25% were college graduates, and 14% had less than high school education. The majority (80%) of depressed probands did not have a current psychiatric illness and had not been receiving psychiatric treatment either at the initial interview or at the second interview. Inclusion into this study required that all subjects had had in-person SADS-L interviews at both points in time.
Diagnostic assessment Diagnostic assessments were conducted by clinically experienced interviewers who had completed a three-month training period in the diagnostic research assessments. The 143 subjects were interviewed directly concerning their psychiatric status on the SADS-L (ENDICOTT and SvrTzvg, 1978), which elicits information relevant to psychiatric disorder over the subject's entire life and enables the recording of all information needed for the application of the RDC (Er~DICOTTand SPITZER, 1979). Included is information on specific symptoms, their duration, age of onset, and the extent to which they impeded the subject's social functioning. In order to enter a specific diagnostic category, subjects had to answer positively to any one of two or three screening questions for that specific diagnostic category. Following the completion of the SADS-L interview, diagnostic estimates (none, probable, definite) were made by the interviewer using RDC criteria. These estimates were based solely on the information obtained during the interview. The presence of a diagnosis includes both definite or probable levels of certainty. For anxiety disorders, we followed the RDC convention of not diagnosing anxiety if it occurred in the context of a major depression. However, we did have information on whether the subject would have met criteria for the anxiety disorder if the depression had not occurred. Between the time of the first and second interview it was quite possible for a new episode of illness to have occurred. Therefore, first episode subsequent to the initial interview is shown as a "new episode". If the first episode in the second interview was subsequent to the initial interview, it was not counted as a disagreement in the Kappa statistic (COHEN, 1960). No age of onset was coded for depressive and antisocial personality disorder. Diagnostic procedures in the first interview were identical to those in the second interview. All interviewers in the second interview were blind to the results of the first interview.
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BmGIT'rE A. PRUSOrF et al.
RESULTS
The time interval between the first and second interview of the 143 subjects ranged from 3 to 6 yr with a mean of about 4.7 yr. There were no significant differences between proband groups and relatives on length of time between interviews. Mean number of yr of followup for normal probands was 4.9, for depressed probands 4.7, and for relatives it was 4.5 yr.
Diagnostic agreement Table 1 presents the cross-classification of the presence or absence of each RDC diagnostic category. Kappa coefficients (CottoN, 1960) are presented when there were at least 10 subjects with a diagnosis at either interview. Test-retest reliability of major depression (x = 0.80), personality (x = 0.66) and panic disorder (x = 0.64) was excellent. Agreement for drug abuse (x = 0.56), general anxiety disorder (GAD) (x = 0.55), depressive personality (~c=0.45), and alcoholism (x=0.41) was good. Agreement for obsessive-compulsive disorders and other phobias was low (x 0.32). Agreement for hyperthymic or cyclothymic personality was not acceptable (Table 1). TABLE I. TEST-RETEST RELIABILITY OF LIFETIME DIAGNOSIS
Diagnoses*
First interview
Second interview
Kappa
Major Depression
No Yes
No 55 5
Yes 9 58
New episode? 16
Antisocial Personality
No Yes
141 0
1 1
Panic Disorder
No Yes
99 5
13 23
3
0.64 :~
Drug Abuse
No Yes
138 3
0 2
0
0.56
Generalized Anxiety Disorder
No Yes
71 11
17 32
12
0.55
Depressive Personality
No Yes
22 9
5 7
Alcoholism
No Yes
127 4
6 4
2
0.41
Obsessive-Compulsive Disorder
No Yes
131 3
6 2
1
0.32~
Phobic Disorder
No Yes
108 7
18 9
1
0.32kt
Hyperthymic or Cyclothymic Personality
No Yes
131 1
11 0
0
N.S.
0.80 ~t
0.66~
0.45 :~
*Probable and definite RDC diagnosis. t A new episode is defined as a first episode of major depression with an age of onset after the initial interview. SP < o.0ol.
LIFETIME PREVALENCEAND AOE OF ONSET TABLE2. RECALLoF
111
I a r E T I ~ PREVALENCE OF MAJOR DEPRESSION BY PR.OBAND AND RELATIVE*
First interview
Group
Second interview No Yes Kappa
z
Normal probands (N= 29)
No Yes
27 0
2 0
Depressed probands (N= 54)
No Yes
0 3
0 51
All probands (iV= 83)
No Yes
27 3
2 51
0.87
7.9
All relatives (N= 44)
No Yes
28 2
7 7
0.48
3.3
*N= 127 subjects; sixteen subjects with first episode of major depression after the first interview are excluded.
Reliability o f major depression in probands and relatives Because the ascertainment schemes and selection criteria differed from probands and relatives, test-retest reliability of major depression in each group was examined separately. Table 2 shows that the test-retest reliability was significantly higher for the probands (x = 0.87) than for the relatives (~ = 0.48). As can be seen, 16 of the 44 relatives received a diagnosis of major depression in either the first a n d / o r the second interview. Thirteen of the 16 (81°70) relatives reported treatment for "emotional illness" at either or both interviews. Test-retest reliability of major depression did not change significantly when treatment for emotional illness was taken into account.
Reliability o f major depression by age and sex The reliability of major depression was also examined by current age by sex of the index case. The levels of agreement between the first and second interview were as follows: ages 18-34 yr, x = 0 . 6 8 ; ages 35-44, x = 0 . 8 2 ; ages 4 5 + , ~ = 0 . 8 1 ; and for males, x = 0 . 7 7 ; females, x = 0.78.
Reliability of age o f onset of psychiatric disorder Table 3 shows the intraclass correlation coefficient for age of onset. Agreement for age TABLE 3. TEST-RETEST RELIABILITY OF RECALL OF AGE OF ONSET
Major Depression Panic Disorder Phobic Disorder Generalized Anxiety Disorder Alcoholism *P < 0.001.
N
Intraclass correlation
58 19 9 32 11
0.71" 0.70* 0.58* 0.55* 0.41"
BRIGITTE A . PRUSOFF et aL
112
of onset ranged from 0.71 for major depression and 0.70 for panic disorder to 0.41 for alcoholism. All values were significant at the P < 0.001 level. Reliability of recall of age of onset of depression between the first and second interview was not affected by sex of the respondent nor whether the respondent was a proband or relative. Reliability of recall of age of onset was lower in respondents with a longer followup period, 5-6 yr as compared to 3-4 yr. In subjects with a follow-up time of under 4 yr the intraclass correlation coefficient was 0.91, and with a follow-up time above 4 yr this coefficient was reduced to 0.51. Reliability of recall of age of onset was affected by age of respondent (Table 4). The older respondents (ages 45-64) as compared to the younger respondents (ages 24-44) reported a later age of onset in the second interview. In the first interview, the mean age of onset for subjects under age 45 was 26.2 yr, which shifted only slightly to 26.6 yr in the second interview. This shift was significantly greater in the older group (mean age of onset 32.2 yr in the first interview to 35.9 yr in the second interview). TABLE 4. RECALL OF AGE OF ONSET OF MAJOR DEPRESSION IN FIRST AND SECOND INTERVIEW BY AGE AT FIRST INTERVIEW (N= 58)
A g e (yr) at first interview 2 4 - 4 4 (N= 32) 4 5 - 6 5 ( N = 26) Total
First interview-~ age o f onset
Second interview-~ age o f onset
Differences
26.2 32.2 28.9
26.6 35.9 30.8
0.3 3.7* 1.9*
* P < 0.001. DISCUSSION
The purpose of this study was to examine the test-retest reliability of reporting lifetime psychiatric diagnosis and age of onset over a 3-5 yr period. The test-retest assessments were made by interviewers who were blind to and independent of the initial assessment. Recall of lifetime prevalence of major depression was excellent. Recall of antisocial personality, panic disorder, drug abuse, GAD, depressive personality, and alcoholism was good. Recall of obsessive-compulsive disorder and phobia was acceptable but lower, whereas the reliability of hyperthymia or cyclothymia was not acceptable. Reliability of recall for major depression did not vary substantially by age or sex of the informant. Recall of lifetime major depression in the probands, all of whom had been treated specifically for depression, was excellent. Although recall of major depression in their relatives was acceptable, it was significantly lower than for the probands. Fewer than 15% of either the probands or the relatives were in a current state of depression at the time of interview so that current symptom state does not explain the differences in agreement over time found between probands and relatives. Treatment p e r s e could not account for the differences in recall between probands and relatives. Eighty percent of the relatives received treatment, although not necessarily for depression, and recall did not vary in relatives by having received treatment. However, all the probands had received treatment specifically for depression in a speciality clinic, which contributed to the better recall in the probands.
LIFETIMEPP,.EVALENCEANDAOEor ONSET
113
The test-retest reliability for the age of onset of major depression and panic disorder was excellent, and for phobia, GAD and alcoholism, was acceptable. Both probands and relatives fairly accurately recalled the age of onset of their depression. However, there was a reduction in agreement over time. Recall after 3-4 yr was better than 5-6 yr. There was a tendency for older respondents to systematically increase the age of onset of their depression across the two interviews, but the increase was only a few yr. Recall of age of onset did not differ significantly by sex of respondent or whether the respondent was a proband or relative. It seems that once subjects recall the history of psychiatric illness they can recall the previously stated age of onset. Comparison with other studies Previous reports on the reliability of lifetime prevalence of psychiatric disorder are presented in Tables 5 and 6. The studies are divided by type of sample, since community and relative samples tend to yield different results than patient samples. As can be seen, test-retest reliability of recall of major depression in patient or mixed samples in all studies, including our own, are excellent. The results for major depression do not vary by diagnostic instrument, SADS-L or DIS, or by diagnostic criteria, DSM-III or RDC. With the exception of the study by I~T.LERet al. (1981) all of the studies had lengthy follow-up periods. The higher reliability of recall of lifetime diagnosis in the patient as compared to the nonpatient samples is consistent with the finding of ORVASCHELet aL (1982) who compared family history diagnosis to direct interview in 696 individuals assessed by SADS-L. They found that sensitivity for depression was increased in subjects who had received treatment. The results in community or relative samples generally yield lower levels of reliability (Table 6). For major depression (with the exception of the Wittchen study), the test-retest results are poor for DIS (ANTI-ION~Yet al., 1985; ROBINSet al., 1981) or PSE (WING et al., 1977), and are better with the SADS. The less structured, more probing, nature of the SADS which allows the interviewer to add questions may be necessary to elicit information from nonpatient samples. However, these findings for the DIS are not consistent for all diagnoses. The DIS, as well was the SADS, had fair to excellent reliability for alcohol and drug abuse. The reliability for GAD and panic disorder ranges between acceptable and poor. The instability of hyperthymia and cyclothymia is consistent with the findings of THOMPSONet al. (1981), who compared family history to direct interview data based on SADS-L and found lower sensitivity for less severe disorders, particularly hyperthymia. Clearly, the data available are limited. While the sample sizes range from 50 to 810, even a community sample of 810 produces an inadequate representation of specific disorders. While comparisons of Kappas between studies with different samples, sample sizes and sampling procedures are problematic due to the sensitivity of the Kappa measure to the base rate of the disorder under study (SPITZNAGELand HELZER,1985), the Kappa statistics still provide investigators working on reliability studies with the best quantification of chance-corrected diagnostic agreement; decrements in Kappa with decreased prevalence accurately reflect the difficulty in reliably assessing rare disorders (SrlROtlT et al., 1987). Base rates for major depression in the studies under discussion were between 20 and 80o70, the range in which Kappa is quite stable, however; base rates for diagnoses other than
BRIGITTE A . PRUSOFF et al.
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LIFETIME PREVALENCE AND AGE OF ONSET
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TABLE 7. TEST-RETEST R E L I A B I L I T Y OF AGE OF ONSET OF PSYCHIATRIC DISORDERS*
Authors
Agreementt G A D Alcohol
N
Retest interval
MDD
391
18 m o n t h s
ANDREASEN et al. (1981)
50
MAzoRE and GERSHON (1979) KELLER et al. (1981) This study
48
a.m. vs p.m. 6 months 6.7 m o n t h s
0.88"~ 0.51§ 1.00 0.64 0.83
25 127
a.m. vs p.m. 4 yr
0.74 0.71
BROMET et al. (1986)
1.00 0.63
0.97 0.95
0.55
0.41
*All studies are based on S A D S / R D C . tEither K a p p a or Intraclass correlations were used. :~1 episode. § > 1 episode.
major depression were much lower, and a larger sample is required for making any valid inferences. It is quite clear that the length of time between test-retest affects reliability. In the study by ANDREASENet al. (1981), who examined 50 relatives of probands, there was a significant decrease in reliability between same day to a six-month follow-up finding. However, the six-month reliability for major depression was still considerably higher than that of the present study (i.e. 0.75 vs 0.47). In the more recent study of BROlVmTet al. (1986), the 18-month test-retest reliability for major depression was quite similar to that observed for the relatives in the present study (i.e. 0.51 vs 0.48). A comparison of the three studies seems to suggest that a longer interval between the test-retest interviews does increase the chance of forgetting a "lifetime diagnosis", at least between the same day, six-month, an 18-month time span. In our 4-yr interval, the agreement was not appreciably reduced from the 18-month interval suggesting that there may be a floor on "forgetting". We could find only four other studies which reported data on test-retest reliability of age of onset of psychiatric disorders. All studies use SADS-RDC so that no statements can be made about the reliability of other methods (Table 7). Reliability of age of onset for major depression is excellent, particularly for single episodes, and does not seem to fluctuate widely by length of retest interval among probands. Reliability of age of onset for alcoholism in the ANDgEASVNet al. (1981) study was higher than in ours, 0.95 vs 0.41, and similar to ours for GAD, 0.63 vs 0.55. Further evidence for the reliabilityof age of onset of major depression has been reported between probands who were directly interviewed and their first-degree relatives who provided family history data. Significant correlations between direct interview and family history were obtained for all types of first-degree relatives and spouses (parents 0.61; spouses 0.65; and adult offspring 0.42). There were no significant differences between direct interview and relative report in the mean age of onset. Differences in mean age of onset ranged from 0.8 yr for offspring to 3.8 yr for siblings. This study indicated that age of onset can be obtained reasonably reliably by family history.
116
BRIGITTE A. PRUSOFF et aL
Implications for family studies The findings suggest that reliability of recall of lifetime prevalence of major depression for probands who have received treatment for depression is excellent and that multiple sources of information are not necessary to assess the proband in family studies. The lifetime reliability of major depression and its age of onset in relatives is less stable. In studies of children at high risk for psychiatric disorders by virtue of having an ill parent, the assessment of the psychiatric status of both parents is essential. These data suggest that the diagnosis of the non-proband parent may not be as stable as that of the proband parent. Moreover, in family studies where relatives are assessed, the reliability of many diagnoses ranges from good to nonacceptable. Recall for major depression does not seem to be affected by the age or sex of the respondent. The recollection of age of onset of most disorders, and especially major depression, is relatively stable over time. Although there was some drift upward for age in older subjects and some drift for longer periods between interviews, the overall agreement between time periods is quite good. The identification of the precise onset of chronic illness is not unique to psychiatric disorders. Our findings on the stability of age of onset is in sharp contrast to the literature on chronic disease epidemiology of nonpsychiatric disorders, which emphasizes the problem of dating onset for chronic conditions (MAus~R and BArry, 1974). It is, of course, possible that while age of onset reported by the subject is reliable, it is not valid. The age of onset of the disorder may not be the first time all the symptoms are present but rather when the first prodromal symptoms are manifest, or, alternately, may be merely a dramatic episode in a longstanding process. Taken together, these findings provide evidence for the use of multiple informants and multiple types of information and interviews (ORvASCHELet al., 1982; THOMPSONet al., 1982) at different time periods in arriving at best estimate diagnosis in relatives (L~cKMA~ et al., 1982). Acknowledgements--This work was supported in part by Alcohol, Drug Abuse, and Mental Health Administration grants MH 28274 and 36197 from the Affective and Anxiety Disorders Research Branch, National Institute of Mental Health, Rockville, Maryland; by Yale Mental Health Clinical Research Center, National Institute of Mental Health grant MH 30929; by the John D. and Catherine T. MacArthur Foundation Mental Health Research Network on Risk and Protective Factors in Major Mental Disorders; and by the John D. and Catherine T. MacArthur Foundation Grant No. 86-212, "Secular changes and cohort effects in rates of major depression." REFERENCES ANDr,.~ASEN, N. C., GROVE, W. M., SHAPmO, R. W. and KELLER, M. B. (1981) Reliability of lifetime diagnosis: a multicenter collaborative perspective. Archs gen. Psychiat. 38, 400-405. ANTHONY, J. C., FOLSTEIN, M., ROMANOSKI,A. J., VON KORFF, M. R., NESTADET,G. R., CHAHAL, R., MERCHANT, A., BROWN, H., SrL~mO, S., KRAm~R, M. and GRtr~NB~Ra, E. M. (1985) Comparison of the lay diagnostic interview schedule and a standardized psychiatric diagnosis: experience in eastern Baltimore. Archs gen. Psychiat. 42, 667-675. BROm~T, E. J., DUNN, L. O., CONNELL, M. M., D~w, M. A. and ScrrOLBER~, H. C. (1986) Long-term reliability of diagnosing lifetime major depression in a community sample. Archs gen. Psychiat. 43, 435-440. COHEN, J. (1960) A coefficient of agreement for nominal scales. Educ. psychol. Measur. 20, 37-46. ENDICOTT, J. and SPITZmt, R. L. (1978) A diagnostic interview: the schedule for affective disorders and schizophrenia. Archs gen. Psychiat. 35, 773-782. ENDICOTT, J. and SPITZ~R, R. L. (1979) Use of the research diagnositc criteria and the schedule for affective disorders and schizophrenia. Am. J. Psychiat. 136, 52-59.
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HELZER, J. E., ROBINS, L. N., McEvoY, L. T., SPITZNAGEL, E. L., STOLTZMAN, R. K., FARMER, A. and BROCKINGTON, I. F. (1985) A comparison of clinical and diagnostic interview schedule diagnoses: physician re-examination of lay-interviewed cases in the general population. Archs gen. Psychiat. 42, 657-666. KELLER, M. B., LAVOm, P. W., A~rDREASEN,N. C. and GRow, W. M. (1981) Test-retest reliability of assessing psychiatrically ill patients in a multi-center design. J. psychiat. Res. 4, 213-227. LECKMAN, J. F., SHOLOMSKAS,D., THOMPSON, W. D., BELANGER,A. and WEISS~tN, M. M. (1982) Best estimate of lifetime psychiatric diagnosis: a methodological study. Archs gen. Psychiat. 39, 879-883. MAUSNER, J. S. and BAHN, A. K. (1974) Epidemiology: A n Introductory Text. W. B. Saunders, Philadelphia. MAZtrRE, C. and GERSHON, E. S. (1979) Blindness and reliability in lifetime psychiatric diagnosis. Archs gen. Psyehiat. 36, 521-525. ORVASCHEL, H., THOMPSON, W. D., BELANGER, k . , PRUSSOFF, B. A. and KIDD, K. K. (1982) Comparison of the family history method to direct interiew: factors affecting the diagnosis of depression. £ affect. D/s. 4, 49-59. ROBINS, L. N., HELZER, J. and CROUGHAN, J. (1981) The NIMH diagnostic interview schedule: its history, characteristics, and validity. Archs gen. Psychiat. 39, 381-389. SHROUT, P. E., SPITZER, R. L. and FLEISS, J. L. (1987) Quantification of agreement in psychiatric diagnosis revisited. Archs gen. Psychiat. 44, 172-177. SPITZNAGEL,E. L. and HELZER, J. E. (1985) A proposed solution to the base rate problem in the Kappa statistic. Archs gen. Psychiat. 42, 725-728. THOMPSON, W. D., ORVASCHEL, H., PRUSOFF, B. A. and KIDD, K. K. (1982) An evaluation of the family history method for ascertaining psychiatric disorders. Archs gen. Psychiat. 39, 53-58. THOMPSON, W. D. and WEISSMAN, M. M. (1981) Quantifying lifetime risk of psychiatric disorder, d. psychiat. Res. 16, 113-126. WEISSMAN,M. M., GERSHON,E. S., KIDD, K. K., PRUSSOFF, B. A., LECKMAN, J. F., DIBBLE,E., HAMOVlT, J., THOMPSON, W. D., PAULS, D. L. and GtmOFF, J. g. (1984a) Psychiatric disorders in the relatives of probands with affective disorders: the Yale-NIMH collaborative family study. Archs gen. Psyehiat. 41, 13-21. WEISSMAN, M. M., KIDD, K. K. and PRUSO~, B. A. (1982) Variability in the rates of affective disorders in the relatives of severe and mild nonbipolar depressives and normals. Archs gen. Psychiat. 39, 1397-1403. WEISSMAN,M. M. and MYERS, J. K. (1978) Affective disorders in a United States commtmity: the uses of research diagnostic criteria in an epidemiological survey. Archs gen. Psychiat. 35, 1304-1311. WEISSMA~, M. M., WICKRAMARATNE,P., MERIKANGAS, K. R., LECKMAN, J. F., PRUSOFF, B. A., CARUSO, K. A., KIDD, K. K. and GAMMON,G. D. (1984b) Onset of major depression in early adulthood: increased familial loading and specificity. Archs gen. Psychiat. 41, 1136-1143. Wise, J. K., COOPER, J. E. and SARTOmUS,N. (1974) Measurement and Classification o f Psychiatric Symptoms: A n Instructional Manual f o r the PSE and CATEGO Program. Cambridge University Press, New York. WINe, J. K., NlXON, J. M., MANN, S. A. and LE~, J. P. (1977) Reliability of the PSE (9th Edu) used in a population study. Psychol. Med. 7, 505-516. WlTTCHEN, H. U., SEMLER, G. and ZERSSEN, V. D. (1985) A comparison of two diagnostic methods: clinical ICD diagnoses vs DSM-III and research diagnostic criteria using the diagnostic interview schedule (Version 2). Archs gen. Psychiat. 42, 677-684.
0022-3956/88 $3.00+ .00 © 1988 Pergamon Press pie
LIFETIME P R E V A L E N C E A N D A G E OF ONSET OF P S Y C H I A T R I C DISORDERS: R E C A L L 4 Y E A R S L A T E R BRIGITTE A. PRUSOFF*, KATHLEEN R. MERIKANGAS*~ a n d MYRNA M. WEISSMAN~ *Department of Psychiatry and "~Departmentof Epidemiology, Yale University School of Medicine, Connecticut Mental Health Center, New Haven, Connecticut, U.S.A.; ~Department of Psychiatry, Collegeof Physicians and Surgeons of Columbia University, New York, New York U.S.A.
(Revised 14 July 1987) Summary--The blind test-retest reliability of lifetime prevalence and age of onset of psychiatric diagnoses, based on the SADS-Linterviewand RDC over a three-to-fiveyear period, was examined in 143 probands and their relatives. Reliability of lifetime prevalence of major depression was excellent;reliabilityof antisocialpersonality,panic disorder, drug abuse, GAD, depressivepersonality, and alcoholism was good; reliability of obsessive-compulsive disorder and phobia was acceptable but lower. The reliability of hyperthymia or cyclothymia was not acceptable. Reliability for major depression did not vary substantially by age or sex of the informant, but recall of major depression was significantly higher in the probands than in their relatives. The testretest reliability for the age of onset of major depression and panic disorder was excellent, and for phobia, GAD and alcoholism, was acceptable. Both probands and relatives recalled the age of onset of their depression fairly accurately. However, there was a reduction in agreement over time. Recall after 3-4 yr was better than 5-6 yr. There was a tendency for older respondents to systematicallyincrease the age of onset of their depression across the two interviews, although the increase was only a few years. Recall of age of onset did not differ significantlyby sex of respondent or whether the respondent was a proband or relative. These findings are discussedin light of several available studies of reliability of lifetime prevalence of psychiatric diagnoses. INTRODUCTION INFORMATION o n the lifetime prevalence o f psychiatric disorders a n d their initial onset is i m p o r t a n t b o t h in clinical practice a n d research. Since the i n t r o d u c t i o n o f s t a n d a r d i z e d psychiatric diagnostic criteria a n d structured diagnostic interviews to assess the signs a n d s y m p t o m s t h a t define the criteria, i n f o r m a t i o n o n the lifetime prevalence a n d the age o f onset o f psychiatric disorders has been o b t a i n e d with increasing frequency. T h e reliability o f assessment o f lifetime diagnosis has i m p r o v e d with the use o f these new diagnostic m e t h o d s . Several studies have assessed the test-retest reliability o f lifetime diagnosis i n patients (I~LLWR et aL, 1981; MAZtrR~ a n d GERSHON, 1979), i n relatives o f patients (ANDR~ASEN et aL, 1981; M A Z m ~ a n d GERSHON, 1979); a n d in c o m m u n i t y samples (ANDREASEN et aL, 1981; ANTI-IONYet aL, 1985; BROMET et aL, 1986; H~.LZER et al., 1985; KELLER et al., 1981; MAZtntE a n d GERSHON, 1979; Wn,rc et aL, 1977; WITTCrmN et al., 1985). I n general, these studies have f o u n d t h a t the reliability is acceptable, p a r t i c u l a r l y for alcohol dependence a n d drug abuse a n d for m a j o r depression i n patient samples (Am)R~ASEN et al., 1981; HV.LZER et aL, 1985; I~LLER et aL, 1981). Better a g r e e m e n t has b e e n observed Address reprint requests to: Brigitte A. Prusoff, Ph.D., Yale University School of Medicine, Department of Psychiatry, 350 Congress Avenue, New Haven, Connecticut, 06519, U.S.A. 107
108
BRIGITTEA. PRUSOrFet aL
among patient samples, and for those diagnoses that were elicited by experienced clinicians rather than by lay interviewers (ANDREASENet aL, 1981; KELLERet al., 1981; WITTCHEr~ et al., 1985). Most studies, with the exception of that of WITTCI-mNet aL (1985), have found that the longer the test-retest interval, the lower the reliability. There appears to be little difference in terms of reliability between the Research Diagnostic Criteria (RDC) and the American Psychiatric Association Diagnostic and Statistical Manuai-3rd Edition (DSMIII), but the reliability of the Psychiatric State Examination (PSE) (WING et al., 1977) and CATEGO (ANTHONYet al., 1985) appeared to be lower than that of the Diagnostic Interview Schedule (DIS) or the Schedule for Affective Disorders and Schizophrenia (SADS) using DSM-III or RDC. Reliability of specific symptoms has also been examined (KELr.ERet al., 1981) and found to be quite acceptable, with the exception of specific delusions and hallucinations. Increasing attention has been given to the reliability of age of onset of disorders, (ANREASENet al., 1981; BROMETet al., 1986; KELLERet al., 1981; MAZUREand GERSI-ION, 1979), since age of onset has been shown to be a predictor of longitudinal impairment and of increased familial aggregation for some disorders (WEIsSMANet al., 1984b). Accurate assignment of the age of onset of a disorder is essential to some classification schemes, such as the primary-secondary convention based on order of presentation of two disorders, and to analytic techniques that apply age-correction to the data. For example, life table analysis yields estimates of lifetime risk (LTR), which refers to the risk for onset of a particular disorder between birth and some particular age, usually the age at interview or the age at death, or the last-known age if the information is obtained from records or by report (THOMPSON and WEISSMAN, 1981). The ideal method for estimating LTR of a disorder is an unobtrusive longitudinal follow-up of persons from birth to death. Since such an approach obviously is not feasible, retrospective assessment of the life course of psychopathology is generally used to estimate lifetime prevalence. If recall of the age at which symptoms of a particular diagnosis first appeared is poor, LTR is also inaccurate. The purpose of this paper is to examine the test-retest reliability of recall of lifetime prevalence and age of onset of psychiatric disorders. The data derive from a family study of major depression in which normal and depressed probands and their first-degree relatives were reinterviewed at two points in time, approximately 4 yr apart (WEISSMANet al., 1982).
METHOD Subjects Subjects for this study were 143 probands, spouses and adult offspring who were originally part of a family-genetic study of affective disorders (WEIsSMANet al., 1982, 1984a) and were reinterviewed approximately 4 yr after their initial entrance into the study. In the original study there were 133 probands with major depression defined according to modified Research Diagnostic Criteria (requiring a 4-week duration of symptoms and impairment in the major social role). The probands had all received treatment at the Yale University Depression Research Unit or at other facilities in the Yale Department of Psychiatry. The 82 normal controls were obtained from the 1975 community survey (WEIsSMAN and MYERS, 1978) and had no history of psychiatric illness based on at least
LIFETIME PREVALENCE AND AGE OF ONSET
109
four direct interviews (the last two using SADS-RDC criteria) over an 8-yr period. All the probands were white and were grouped matched by age and sex. The original study did not include direct interviews of offspring under 18 yr of age. A direct-interview study of children was initiated 6 yr after the original study had begun, and all probands who had offspring under age 18 at the time of the original proband interview were contacted and asked to be reinterviewed. In order to determine the current and past clinical status of the parents and the older siblings of these children, the adults were interviewed separately by independent interviewers and comprise the sample for this study. The 143 subjects included 54 probands with a lifetime diagnosis of major depression, 33 normal control probands without any prior episodes of psychiatric illness, 44 of their spouses, and 12 of their offspring over age 17. The mean age of the probands and their spouses was 40 yr at the time of the initial interview and the mean age of the offspring was 19 yr; 59% of the sample were female, 25% were college graduates, and 14% had less than high school education. The majority (80%) of depressed probands did not have a current psychiatric illness and had not been receiving psychiatric treatment either at the initial interview or at the second interview. Inclusion into this study required that all subjects had had in-person SADS-L interviews at both points in time.
Diagnostic assessment Diagnostic assessments were conducted by clinically experienced interviewers who had completed a three-month training period in the diagnostic research assessments. The 143 subjects were interviewed directly concerning their psychiatric status on the SADS-L (ENDICOTT and SvrTzvg, 1978), which elicits information relevant to psychiatric disorder over the subject's entire life and enables the recording of all information needed for the application of the RDC (Er~DICOTTand SPITZER, 1979). Included is information on specific symptoms, their duration, age of onset, and the extent to which they impeded the subject's social functioning. In order to enter a specific diagnostic category, subjects had to answer positively to any one of two or three screening questions for that specific diagnostic category. Following the completion of the SADS-L interview, diagnostic estimates (none, probable, definite) were made by the interviewer using RDC criteria. These estimates were based solely on the information obtained during the interview. The presence of a diagnosis includes both definite or probable levels of certainty. For anxiety disorders, we followed the RDC convention of not diagnosing anxiety if it occurred in the context of a major depression. However, we did have information on whether the subject would have met criteria for the anxiety disorder if the depression had not occurred. Between the time of the first and second interview it was quite possible for a new episode of illness to have occurred. Therefore, first episode subsequent to the initial interview is shown as a "new episode". If the first episode in the second interview was subsequent to the initial interview, it was not counted as a disagreement in the Kappa statistic (COHEN, 1960). No age of onset was coded for depressive and antisocial personality disorder. Diagnostic procedures in the first interview were identical to those in the second interview. All interviewers in the second interview were blind to the results of the first interview.
110
BmGIT'rE A. PRUSOrF et al.
RESULTS
The time interval between the first and second interview of the 143 subjects ranged from 3 to 6 yr with a mean of about 4.7 yr. There were no significant differences between proband groups and relatives on length of time between interviews. Mean number of yr of followup for normal probands was 4.9, for depressed probands 4.7, and for relatives it was 4.5 yr.
Diagnostic agreement Table 1 presents the cross-classification of the presence or absence of each RDC diagnostic category. Kappa coefficients (CottoN, 1960) are presented when there were at least 10 subjects with a diagnosis at either interview. Test-retest reliability of major depression (x = 0.80), personality (x = 0.66) and panic disorder (x = 0.64) was excellent. Agreement for drug abuse (x = 0.56), general anxiety disorder (GAD) (x = 0.55), depressive personality (~c=0.45), and alcoholism (x=0.41) was good. Agreement for obsessive-compulsive disorders and other phobias was low (x 0.32). Agreement for hyperthymic or cyclothymic personality was not acceptable (Table 1). TABLE I. TEST-RETEST RELIABILITY OF LIFETIME DIAGNOSIS
Diagnoses*
First interview
Second interview
Kappa
Major Depression
No Yes
No 55 5
Yes 9 58
New episode? 16
Antisocial Personality
No Yes
141 0
1 1
Panic Disorder
No Yes
99 5
13 23
3
0.64 :~
Drug Abuse
No Yes
138 3
0 2
0
0.56
Generalized Anxiety Disorder
No Yes
71 11
17 32
12
0.55
Depressive Personality
No Yes
22 9
5 7
Alcoholism
No Yes
127 4
6 4
2
0.41
Obsessive-Compulsive Disorder
No Yes
131 3
6 2
1
0.32~
Phobic Disorder
No Yes
108 7
18 9
1
0.32kt
Hyperthymic or Cyclothymic Personality
No Yes
131 1
11 0
0
N.S.
0.80 ~t
0.66~
0.45 :~
*Probable and definite RDC diagnosis. t A new episode is defined as a first episode of major depression with an age of onset after the initial interview. SP < o.0ol.
LIFETIME PREVALENCEAND AOE OF ONSET TABLE2. RECALLoF
111
I a r E T I ~ PREVALENCE OF MAJOR DEPRESSION BY PR.OBAND AND RELATIVE*
First interview
Group
Second interview No Yes Kappa
z
Normal probands (N= 29)
No Yes
27 0
2 0
Depressed probands (N= 54)
No Yes
0 3
0 51
All probands (iV= 83)
No Yes
27 3
2 51
0.87
7.9
All relatives (N= 44)
No Yes
28 2
7 7
0.48
3.3
*N= 127 subjects; sixteen subjects with first episode of major depression after the first interview are excluded.
Reliability o f major depression in probands and relatives Because the ascertainment schemes and selection criteria differed from probands and relatives, test-retest reliability of major depression in each group was examined separately. Table 2 shows that the test-retest reliability was significantly higher for the probands (x = 0.87) than for the relatives (~ = 0.48). As can be seen, 16 of the 44 relatives received a diagnosis of major depression in either the first a n d / o r the second interview. Thirteen of the 16 (81°70) relatives reported treatment for "emotional illness" at either or both interviews. Test-retest reliability of major depression did not change significantly when treatment for emotional illness was taken into account.
Reliability o f major depression by age and sex The reliability of major depression was also examined by current age by sex of the index case. The levels of agreement between the first and second interview were as follows: ages 18-34 yr, x = 0 . 6 8 ; ages 35-44, x = 0 . 8 2 ; ages 4 5 + , ~ = 0 . 8 1 ; and for males, x = 0 . 7 7 ; females, x = 0.78.
Reliability of age o f onset of psychiatric disorder Table 3 shows the intraclass correlation coefficient for age of onset. Agreement for age TABLE 3. TEST-RETEST RELIABILITY OF RECALL OF AGE OF ONSET
Major Depression Panic Disorder Phobic Disorder Generalized Anxiety Disorder Alcoholism *P < 0.001.
N
Intraclass correlation
58 19 9 32 11
0.71" 0.70* 0.58* 0.55* 0.41"
BRIGITTE A . PRUSOFF et aL
112
of onset ranged from 0.71 for major depression and 0.70 for panic disorder to 0.41 for alcoholism. All values were significant at the P < 0.001 level. Reliability of recall of age of onset of depression between the first and second interview was not affected by sex of the respondent nor whether the respondent was a proband or relative. Reliability of recall of age of onset was lower in respondents with a longer followup period, 5-6 yr as compared to 3-4 yr. In subjects with a follow-up time of under 4 yr the intraclass correlation coefficient was 0.91, and with a follow-up time above 4 yr this coefficient was reduced to 0.51. Reliability of recall of age of onset was affected by age of respondent (Table 4). The older respondents (ages 45-64) as compared to the younger respondents (ages 24-44) reported a later age of onset in the second interview. In the first interview, the mean age of onset for subjects under age 45 was 26.2 yr, which shifted only slightly to 26.6 yr in the second interview. This shift was significantly greater in the older group (mean age of onset 32.2 yr in the first interview to 35.9 yr in the second interview). TABLE 4. RECALL OF AGE OF ONSET OF MAJOR DEPRESSION IN FIRST AND SECOND INTERVIEW BY AGE AT FIRST INTERVIEW (N= 58)
A g e (yr) at first interview 2 4 - 4 4 (N= 32) 4 5 - 6 5 ( N = 26) Total
First interview-~ age o f onset
Second interview-~ age o f onset
Differences
26.2 32.2 28.9
26.6 35.9 30.8
0.3 3.7* 1.9*
* P < 0.001. DISCUSSION
The purpose of this study was to examine the test-retest reliability of reporting lifetime psychiatric diagnosis and age of onset over a 3-5 yr period. The test-retest assessments were made by interviewers who were blind to and independent of the initial assessment. Recall of lifetime prevalence of major depression was excellent. Recall of antisocial personality, panic disorder, drug abuse, GAD, depressive personality, and alcoholism was good. Recall of obsessive-compulsive disorder and phobia was acceptable but lower, whereas the reliability of hyperthymia or cyclothymia was not acceptable. Reliability of recall for major depression did not vary substantially by age or sex of the informant. Recall of lifetime major depression in the probands, all of whom had been treated specifically for depression, was excellent. Although recall of major depression in their relatives was acceptable, it was significantly lower than for the probands. Fewer than 15% of either the probands or the relatives were in a current state of depression at the time of interview so that current symptom state does not explain the differences in agreement over time found between probands and relatives. Treatment p e r s e could not account for the differences in recall between probands and relatives. Eighty percent of the relatives received treatment, although not necessarily for depression, and recall did not vary in relatives by having received treatment. However, all the probands had received treatment specifically for depression in a speciality clinic, which contributed to the better recall in the probands.
LIFETIMEPP,.EVALENCEANDAOEor ONSET
113
The test-retest reliability for the age of onset of major depression and panic disorder was excellent, and for phobia, GAD and alcoholism, was acceptable. Both probands and relatives fairly accurately recalled the age of onset of their depression. However, there was a reduction in agreement over time. Recall after 3-4 yr was better than 5-6 yr. There was a tendency for older respondents to systematically increase the age of onset of their depression across the two interviews, but the increase was only a few yr. Recall of age of onset did not differ significantly by sex of respondent or whether the respondent was a proband or relative. It seems that once subjects recall the history of psychiatric illness they can recall the previously stated age of onset. Comparison with other studies Previous reports on the reliability of lifetime prevalence of psychiatric disorder are presented in Tables 5 and 6. The studies are divided by type of sample, since community and relative samples tend to yield different results than patient samples. As can be seen, test-retest reliability of recall of major depression in patient or mixed samples in all studies, including our own, are excellent. The results for major depression do not vary by diagnostic instrument, SADS-L or DIS, or by diagnostic criteria, DSM-III or RDC. With the exception of the study by I~T.LERet al. (1981) all of the studies had lengthy follow-up periods. The higher reliability of recall of lifetime diagnosis in the patient as compared to the nonpatient samples is consistent with the finding of ORVASCHELet aL (1982) who compared family history diagnosis to direct interview in 696 individuals assessed by SADS-L. They found that sensitivity for depression was increased in subjects who had received treatment. The results in community or relative samples generally yield lower levels of reliability (Table 6). For major depression (with the exception of the Wittchen study), the test-retest results are poor for DIS (ANTI-ION~Yet al., 1985; ROBINSet al., 1981) or PSE (WING et al., 1977), and are better with the SADS. The less structured, more probing, nature of the SADS which allows the interviewer to add questions may be necessary to elicit information from nonpatient samples. However, these findings for the DIS are not consistent for all diagnoses. The DIS, as well was the SADS, had fair to excellent reliability for alcohol and drug abuse. The reliability for GAD and panic disorder ranges between acceptable and poor. The instability of hyperthymia and cyclothymia is consistent with the findings of THOMPSONet al. (1981), who compared family history to direct interview data based on SADS-L and found lower sensitivity for less severe disorders, particularly hyperthymia. Clearly, the data available are limited. While the sample sizes range from 50 to 810, even a community sample of 810 produces an inadequate representation of specific disorders. While comparisons of Kappas between studies with different samples, sample sizes and sampling procedures are problematic due to the sensitivity of the Kappa measure to the base rate of the disorder under study (SPITZNAGELand HELZER,1985), the Kappa statistics still provide investigators working on reliability studies with the best quantification of chance-corrected diagnostic agreement; decrements in Kappa with decreased prevalence accurately reflect the difficulty in reliably assessing rare disorders (SrlROtlT et al., 1987). Base rates for major depression in the studies under discussion were between 20 and 80o70, the range in which Kappa is quite stable, however; base rates for diagnoses other than
BRIGITTE A . PRUSOFF et al.
114
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LIFETIME PREVALENCE AND AGE OF ONSET
115
TABLE 7. TEST-RETEST R E L I A B I L I T Y OF AGE OF ONSET OF PSYCHIATRIC DISORDERS*
Authors
Agreementt G A D Alcohol
N
Retest interval
MDD
391
18 m o n t h s
ANDREASEN et al. (1981)
50
MAzoRE and GERSHON (1979) KELLER et al. (1981) This study
48
a.m. vs p.m. 6 months 6.7 m o n t h s
0.88"~ 0.51§ 1.00 0.64 0.83
25 127
a.m. vs p.m. 4 yr
0.74 0.71
BROMET et al. (1986)
1.00 0.63
0.97 0.95
0.55
0.41
*All studies are based on S A D S / R D C . tEither K a p p a or Intraclass correlations were used. :~1 episode. § > 1 episode.
major depression were much lower, and a larger sample is required for making any valid inferences. It is quite clear that the length of time between test-retest affects reliability. In the study by ANDREASENet al. (1981), who examined 50 relatives of probands, there was a significant decrease in reliability between same day to a six-month follow-up finding. However, the six-month reliability for major depression was still considerably higher than that of the present study (i.e. 0.75 vs 0.47). In the more recent study of BROlVmTet al. (1986), the 18-month test-retest reliability for major depression was quite similar to that observed for the relatives in the present study (i.e. 0.51 vs 0.48). A comparison of the three studies seems to suggest that a longer interval between the test-retest interviews does increase the chance of forgetting a "lifetime diagnosis", at least between the same day, six-month, an 18-month time span. In our 4-yr interval, the agreement was not appreciably reduced from the 18-month interval suggesting that there may be a floor on "forgetting". We could find only four other studies which reported data on test-retest reliability of age of onset of psychiatric disorders. All studies use SADS-RDC so that no statements can be made about the reliability of other methods (Table 7). Reliability of age of onset for major depression is excellent, particularly for single episodes, and does not seem to fluctuate widely by length of retest interval among probands. Reliability of age of onset for alcoholism in the ANDgEASVNet al. (1981) study was higher than in ours, 0.95 vs 0.41, and similar to ours for GAD, 0.63 vs 0.55. Further evidence for the reliabilityof age of onset of major depression has been reported between probands who were directly interviewed and their first-degree relatives who provided family history data. Significant correlations between direct interview and family history were obtained for all types of first-degree relatives and spouses (parents 0.61; spouses 0.65; and adult offspring 0.42). There were no significant differences between direct interview and relative report in the mean age of onset. Differences in mean age of onset ranged from 0.8 yr for offspring to 3.8 yr for siblings. This study indicated that age of onset can be obtained reasonably reliably by family history.
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BRIGITTE A. PRUSOFF et aL
Implications for family studies The findings suggest that reliability of recall of lifetime prevalence of major depression for probands who have received treatment for depression is excellent and that multiple sources of information are not necessary to assess the proband in family studies. The lifetime reliability of major depression and its age of onset in relatives is less stable. In studies of children at high risk for psychiatric disorders by virtue of having an ill parent, the assessment of the psychiatric status of both parents is essential. These data suggest that the diagnosis of the non-proband parent may not be as stable as that of the proband parent. Moreover, in family studies where relatives are assessed, the reliability of many diagnoses ranges from good to nonacceptable. Recall for major depression does not seem to be affected by the age or sex of the respondent. The recollection of age of onset of most disorders, and especially major depression, is relatively stable over time. Although there was some drift upward for age in older subjects and some drift for longer periods between interviews, the overall agreement between time periods is quite good. The identification of the precise onset of chronic illness is not unique to psychiatric disorders. Our findings on the stability of age of onset is in sharp contrast to the literature on chronic disease epidemiology of nonpsychiatric disorders, which emphasizes the problem of dating onset for chronic conditions (MAus~R and BArry, 1974). It is, of course, possible that while age of onset reported by the subject is reliable, it is not valid. The age of onset of the disorder may not be the first time all the symptoms are present but rather when the first prodromal symptoms are manifest, or, alternately, may be merely a dramatic episode in a longstanding process. Taken together, these findings provide evidence for the use of multiple informants and multiple types of information and interviews (ORvASCHELet al., 1982; THOMPSONet al., 1982) at different time periods in arriving at best estimate diagnosis in relatives (L~cKMA~ et al., 1982). Acknowledgements--This work was supported in part by Alcohol, Drug Abuse, and Mental Health Administration grants MH 28274 and 36197 from the Affective and Anxiety Disorders Research Branch, National Institute of Mental Health, Rockville, Maryland; by Yale Mental Health Clinical Research Center, National Institute of Mental Health grant MH 30929; by the John D. and Catherine T. MacArthur Foundation Mental Health Research Network on Risk and Protective Factors in Major Mental Disorders; and by the John D. and Catherine T. MacArthur Foundation Grant No. 86-212, "Secular changes and cohort effects in rates of major depression." REFERENCES ANDr,.~ASEN, N. C., GROVE, W. M., SHAPmO, R. W. and KELLER, M. B. (1981) Reliability of lifetime diagnosis: a multicenter collaborative perspective. Archs gen. Psychiat. 38, 400-405. ANTHONY, J. C., FOLSTEIN, M., ROMANOSKI,A. J., VON KORFF, M. R., NESTADET,G. R., CHAHAL, R., MERCHANT, A., BROWN, H., SrL~mO, S., KRAm~R, M. and GRtr~NB~Ra, E. M. (1985) Comparison of the lay diagnostic interview schedule and a standardized psychiatric diagnosis: experience in eastern Baltimore. Archs gen. Psychiat. 42, 667-675. BROm~T, E. J., DUNN, L. O., CONNELL, M. M., D~w, M. A. and ScrrOLBER~, H. C. (1986) Long-term reliability of diagnosing lifetime major depression in a community sample. Archs gen. Psychiat. 43, 435-440. COHEN, J. (1960) A coefficient of agreement for nominal scales. Educ. psychol. Measur. 20, 37-46. ENDICOTT, J. and SPITZmt, R. L. (1978) A diagnostic interview: the schedule for affective disorders and schizophrenia. Archs gen. Psychiat. 35, 773-782. ENDICOTT, J. and SPITZ~R, R. L. (1979) Use of the research diagnositc criteria and the schedule for affective disorders and schizophrenia. Am. J. Psychiat. 136, 52-59.
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