Declining-Effects Models are relevant only if there is empirical support for declining-effects patterns in nature. To test for such patterns, we use TMAP data for 267 adult patients with a Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnosis of bipolar disorder (American Psychiatric Association 1994
). All subjects had signed informed consent, provided baseline and at least one follow-up IDSC assessment, and had been assigned to one of 4 ALGO clinics (n
=141) or 7 TAU clinics (n
=126). The sample was diverse ethnically (27 percent Hispanic, 12 percent African American, 60 percent Caucasian, and 1 percent other), with a mean age of 39.0 years (SD=10.3), and 68 percent female, 24 percent married, 26 percent living alone with household sizes averaging 1.7 plus patient (SD=1.8), were high school graduates (78 percent), but mostly unemployed (73.6 percent) with mean monthly household disposable income (after housing costs) of $450/month (SD=$599) (1999 US$), with income assistance or food-stamps (49 percent) and on Medicaid during six months prior to baseline (53 percent). Clinically, patients at baseline reported a mean length of illness of 14.7 years (SD=12.5), IDSC score of 30.9 (SD=14.5), 24-item Brief Psychiatric Rating Scale (BPRS24
) (Overall and Gorham 1988
; Ventura et al. 1993
) of 52.8 (SD=13.5), and Medical Outcome Study 12-item Short Form (SF-12) (Ware, Kosinski, and Keller 1996
) mental functioning of 35.0 (SD=11.3) and physical functioning of 42.6 (SD=11.6), with 20 percent reporting substance abuse during the prior six months. A 10-item Patient Perception of Benefits scale was constructed for TMAP to measure patient attitudes concerning whether health care can improve patient functioning. Patients were asked “If I can get the help I need from a doctor, I believe that I will be much better able to …manage problems at home, earn a living or go to school, enjoy things that interest me, feel good about myself, handle emergencies and crises, get along with friends, get along with my family, control my life, do things on my own, and make important decisions that affect my life and my family.” Patients ranked each item as strongly agree (=1) to strongly disagree (=5). For this sample, baseline scores ranged from 10 to 50, with mean 19.1 (SD=7.6), with higher scores indicating greater pessimism about care.
Declining-Effects Models (equation 8b
) were estimated using HLM/3L software (Bryk, Raudenbush, and Congdon 1996
) with subjects grouped by baseline symptoms into very severe (IDSC≥46, n
=48), severe (IDSC 17–45, n
=170), and mild (IDSC≤16, n
=46). Estimates were adjusted to reflect patient differences in baseline BPRS24
score, age (years), family size, disposable income, years of education, patient perception of benefits, gender, African American status, and Hispanic status.
Results are reported in . Examining only those subjects who began the study with the most severe depressive symptoms at baseline, patients in both TAU and DMP tracks experienced a reduction in symptoms during the initial three months of the program by –6 IDSC and –16.5 IDSC, respectively. The greater reduction in symptoms during the initial period among DMP patients (DMP initial-effect) was significant (−10.5 IDSC), indicating a more favorable DMP outcome than TAU at the end of the initial period. During the postperiod, however, TAU patients continued to improve at a growth-rate of –3.2 IDSC/qtr, while symptoms for DMP patients were unchanged. The difference in growth-rates was significant (DMP growth-effect) suggesting that TAU patients caught up with their DMP counterparts during the postperiod as IDSC outcome differences between tracks diminished by 3.7 IDSC/qtr.
IDSC Adjusted Estimates of Initial-Change, Growth-Rate, and Differences between DMP and TAU Patients with Bipolar Disorder, by Baseline IDSC Scores
In contrast, patients who entered the study with severe baseline depressive symptoms showed only modest reductions in symptoms after the initial period (–3.7 IDSC for DMP and –2.6 IDSC for TAU), though DMP and TAU differences were not significant. On the other hand, patients with mild symptoms actually showed a worsening of symptoms at the end of the initial period as both DMP and TAU patients regressed into depressive symptom episodes. An apparent inverse relationship between initial reductions and baseline symptoms suggest a regression to the mean confound. The impact on DMP initial- and growth-effects is small, as baseline IDSC values were 30.3±14.5 for DMP and 31.5±14.5 for TAU, or a mean difference of −1.2±1.8 (t=0.67, df=261, p=.51).
In summary, DMP versus TAU exhibited a declining-effects pattern for only the very severely depressed patients.