LD-AGE DEPRESSION IS WIDEspread, affecting at least 1 in 6 patients in general medical practice and an even higher percentage in hospitals and nursing homes. 1-3 Depression, especially in later life, has serious health consequences, including increased health care costs, 4 increased mortality related to suicide 5 and medical illness, 6,7 and amplification of disability associated with medical and cognitive disorders. 8 A recent study by the World Health Organization concluded that unipolar major depression and suicide accounted for 5.1% of the total global burden of disease in 1990, making depression the fourth most important cause of global burden of disability. 9 The study also showed that the significance of illness burden attributable to depression increases with age weighting and is projected to grow further by the year 2020, based on demographic shifts toward a greater proportion of aging adults in the population, especially of the very old.

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Longitudinal studies have a prominent role in psychiatric research; however, statistical methods for analyzing these data are rarely commensurate with the effort involved in their acquisition. Frequently the majority of data are discarded and a simple end-point analysis is performed. In other cases, so called repeated-measures analysis of variance procedures are used with little regard to their restrictive and often unrealistic assumptions and the effect of missing data on the statistical properties of their estimates. We explored the unique features of longitudinal psychiatric data from both statistical and conceptual perspectives. We used a family of statistical models termed random regression models that provide a more realistic approach to analysis of longitudinal psychiatric data. Random regression models provide solutions to commonly observed problems of missing data, serial correlation, time-varying covariates, and irregular measurement occasions, and they accommodate systematic person-specific deviations from the average time trend. Properties of these models were compared with traditional approaches at a conceptual level. The approach was then illustrated in a new analysis of the National Institute of Mental Health Treatment of Depression Collaborative Research Program dataset, which investigated two forms of psychotherapy, pharmacotherapy with clinical management, and a placebo with clinical management control. Results indicated that both person-specific effects and serial correlation play major roles in the longitudinal psychiatric response process. Ignoring either of these effects produces misleading estimates of uncertainty that form the basis of statistical tests of hypotheses.

In the NIMH Treatment of Depression Collaborative Research Program (TDCRP), 250 depressed outpatients were randomly assigned to interpersonal psychotherapy, cognitive-behavioral therapy, imipramine plus clinical management, or pill placebo plus clinical management treatments. Although all treatments demonstrated significant symptom reduction with few differences in general outcomes, an important question concerned possible effects specific to each treatment. The therapies differ in rationale and procedures, suggesting that mode-specific effects may differ among treatments, each of which was precisely specified, applied appropriately, and shown to be discriminable. Outcome measures were selected for presumed sensitivity to the different treatments. Findings provided only scattered and relatively insubstantial support for mode-specific differences. None of the therapies produced consistent effects on measures related to its theoretical origins.

This study reports on the relationship of therapist competence to the outcome of cognitive-behavioral treatment in the National Institute of Mental Health Treatment of Depression Collaborative Research Program. Outpatients suffering from major depressive disorder were treated by cognitive-behavioral therapists at each of 3 U.S. sites using a format of 20 sessions in 16 weeks. Findings provide some support for the relationship of therapist competence (as measured by the Cognitive Therapy Scale) to reduction of depressive symptomatology when controlling for therapist adherence and facilitative conditions. The results are, however, not as strong or consistent as expected. The component of competence that was most highly related to outcome is a factor that reflects the therapist's ability to structure the treatment.