Thirty-four women were enrolled and randomized to group counseling by phone (n=16) or individual counseling by phone (n=18). Retention was not significantly different for group and individual conditions; 85.3% of participants completed assessments at Week 16 and 79.4% at Week 24 (see ). Completers were defined as women who attended at least 70% of treatment sessions and completed at least one follow-up assessment. Compared to drop-outs, completers were significantly older (M=51.0, SD=9.4 years vs. M=30.6, SD=4.8 years, p<.01). No other significant differences in baseline characteristics were found between completers and drop-outs.
Participants were on average 48.0±11.5 years old and had a mean BMI of 34.4 (SD=4.6. No significant differences in baseline characteristics were found across conditions (see ).
Baseline participant characteristics.
Attendance rates to treatment sessions were marginally greater for individual compared to group (including drop-outs, M=88% and 74% of sessions, respectively, p=.08; excluding drop-outs, M=94% and 88%, respectively, p=.08).
3.1. Weight changes
presents weight changes for the completers. A 2 (treatment conditions)×3 (time periods) repeated measures multivariate analysis of variance (MANOVA) indicated a significant main effect for time, F(2,24)=124.8, p<.001, partial η2=.91, and a significant treatment × time interaction, F(2,24)=3.87, p=.035, partial η2=.24. Follow-up univariate ANOVAs indicated that compared to the individual condition, participants in the group condition showed greater weight loss from Baseline to week 16 (p=.01), from Baseline to Week 24 (p=.01), and marginally greater weight loss from week 16 to week 24 (p=.10). Pairwise comparisons across time showed that both conditions had significant weight loss from baseline to week 16 (both ps<.001), but only the group condition showed significant weight loss from week 16 to week 24 (p=.009).
Mean net weight changes (kg) by condition for completers.
For the total sample, assuming no weight change for missing data, repeated measures MANOVA indicated a significant main effect for time, F(2,31)=35.60, p<.001; the main effect for treatment and the interaction effect for treatment × time were not significant. For the group versus individual conditions, weight loss from baseline to Week 24 was 10.1 kg (SD=8.2) vs. 8.3 kg (SD=6.0), respectively. Among the total sample, 62% of group participants achieved the clinical recommendation of 10% weight loss, compared to 50% of individual participants.
3.2. Diet, physical activity, and psychosocial outcomes
We also explored potential dietary, physical activity, and psychosocial contributors to the differences in weight loss between completers in the group and individual conditions. For dietary and physical activity measures, repeated measures MANOVAs showed main effects for time, but no significant interaction effects for treatment × time. From Baseline to Week 24, participants in the group and individual conditions decreased their daily caloric intake by 427kcals (SD=321) and 542kcals (SD=623), decreased their fat consumption by 12.3 % (SD=9.9) and 11.9% (SD=11.4), increased their fruit and vegetable consumption by 3.1 servings (SD=2.1) and 2.9 servings (SD=4.7), and increased their physical activity by 747 METS (SD=1149) and 508 METS (SD=782), respectively (all ps for time <.001).
Participants in group and individual conditions both showed improvements in self-efficacy for controlling diet and problem-solving skills (ps for time <.001 and .05, respectively); however, treatment× time interaction effects were non-significant. Between-subjects t-tests on participant ratings of their working relationship with their counselor (Working Alliance Inventory at Week 16) revealed that participants in the group condition evaluated their working relationship with their counselor more favorably than participants in the individual condition. Participants in the group condition reported greater agreement on goals, greater agreement on how to achieve those goals, and a stronger personal bond with their counselor (all ps<.05).
We also explored whether participants being matched to their preferred treatment modality (group versus individual) impacted weight loss. Prior to randomization, 76% of participants reported that they preferred individual treatment. Thus, 72% of participants who were randomized to individual treatment received their preferred treatment, compared to 20% of participants who were randomized to group treatment. A 2 (treatment condition)×2 (match to preference) univariate analysis of variance on weight change at Week 24 indicated a non-significant main effect for preference match and a non-significant interaction effect between treatment condition and preference match, indicating that match to treatment preference did not influence weight loss outcomes. These results were similar for both completers and intent-to-treat analyses.
shows provider and participant costs for group and individual counseling. Individual counseling incurred higher costs for provider time in preparation/record keeping and in counseling sessions. Group counseling incurred higher costs for phone charges due to higher fees for conference call technology. Participant costs for time in session were higher for group counseling because group calls lasted on average 64 min per session compared to 34 min for individual sessions. Overall, provider and participant costs combined were lower for group counseling. Using the percentage of participants who achieved 10% weight loss in intent-to-treat analysis, cost-effectiveness from a program plus participant perspective (average cost per successful participant) was $714 for group counseling and $1029 for individual counseling. Thus, group treatment dominated individual treatment; it was less expensive and more effective.
Program and participant costs.