Accuracy in reporting past psychiatric symptoms: the role of cross-sectional studies in psychiatric research.

Cross-sectional studies remain a major source of data for research, practice, andpolicy, despitewell-known limitationsof this approach in assessing psychopathology. Such studies are especially valuablewhen the intent is to identify current or recent cases and in repeated studies where trends in rates can be examined. Yet, how well do they identify psychiatric symptoms and syndromes from the past? This is not a trivial questionbecause the accuracy of such classification is important for association studies and, in particular, for clinical neuroscience and genetic studies where the accuracy of phenotypic classification is essential todetermining the relationship of predictors and purported outcomes. Taken at face value, Takayanagi et al1 demonstrate that cross-sectional studies are much worse than longitudinal in identifying a history of psychiatric disorders. The authors find marked underestimates in lifetime prevalence estimates from a single cross-sectional study, and this lack of agreement with psychiatric symptom reporting across thewaves of interviews is remarkable.Among thosewho receivedadiagnosis inaprior wave, 92% of those with obsessive-compulsive disorder and about two-thirdsof thosewithmajordepressivedisorder,panic disorder, andsubstanceabuseordependence (bothalcoholand other drugs) did not report diagnostic symptoms sufficient for a diagnosis at the fourth interview. Also, somewhat surprisingly, recent receipt of mental health services made little difference in the accuracy of reporting of lifetime symptoms. Undoubtedly, a longitudinal study design has many advantages for inquiry: clear separationof riskandoutcomevariables, repeatedmeasurement of psychopathology to identify acute/temporary and chronic symptom patterns, and less reliance on long-term memory for reports. Similarly, assessment that includesmultipledistinct informants (typical inchild psychiatrywhere parents and teachers are routinely queried) can improvediagnostic coverage.2 The key issue for researchers is to determinewhen this additional information is worth the extra effort (and time) to acquire. A secondary and intriguing question addressed by Takayanagi and colleagues is whether there is something unique aboutmental illnesses thatmakes them particularly prone to poor recall comparedwith identifyingphysical ailments.Their results suggest that physical conditions are much more consistently reported thanmental illnesses.However, absent from the conclusions by Takayanagi and colleagues regarding the differencesbetweenaccuracyofpsychiatricdisorders and that of physical conditions is a discussion about the differences in the approachused to classify thephysical comparedwithpsychiatric conditions. The measures that provide the building blocks of psychiatric diagnosis in this study are reports of individual symptoms. TheDSMdiagnoses are constructed post hoc by the researchers based on the endorsement of a grouping of self-reported symptoms without any explicit discussionwith the studyparticipant about adiagnostic label. Physical conditions, on the other hand, aremeasured based on the respondent’s self-report of a diagnosis, presumably because a physician has diagnosed and informed them to that effect. It is clear that long-term recall of psychiatric symptoms has weaknesses, but is it reallyworse than recall of physical symptoms?Arepsychiatric disorders reported ashavingbeengiven by a physician different from report of physician-diagnosed physical conditions? We just do not know. Nevertheless, the important message about the limitations of recall of earlier symptoms is significant and suggests particular caution in interpreting lifetime diagnoses that may rely on reports of earlier symptoms. Results documented by the authors should be considered in thecontextofothermethodological issuesaswell, such as participant retention, case severity, and subthreshold diagnoses. The overall 53% follow-up rate at the wave 4 interviewsuggests thepossibility that those lost to follow-upmight have been the more severe cases, for whom case agreement between cumulative and retrospective estimates might have been greater. In addition, less severe cases could easily fall to subthreshold if only a single clinical feature is forgotten. Neither the number of clinical features endorsed toward a particularDSM diagnosis nor the frequency of subthreshold and barely threshold cases is reported. Might these or other biases influence the results? Possibly, although it is doubtful that differential attritionor othermethodological issues could account for the 3to 4-fold difference in rates identified by the authors. In addition, thoughtful sensitivity analyses examining the importanceof the change indiagnostic systems across thewaves of follow-up and thepotential influenceofcognitiveimpairmentonfindingsareallessential inensuringtheunderlyingvalidityof thefindings.Althoughthis is the first studyof the issueof recalled lifetimediagnosis comparedwithprospectivelyascertaineddiagnosis inadults, theresults are quite consistentwith thedifferences in cumulative vs cross-sectional lifetime rates in adolescents and young adults instudiesbyCopelandetal3 andMoffittetal.4Thus,weareconfident thatTakayanagi andcolleagueshave identifieda significant concern, andweareencouraged to reexaminehowweuse the results from cross-sectional surveys. Related article page 273 Opinion