Trajectory analyses in alcohol treatment research

Abstract

Background: Various statistical methods have been used for data analysis in alcohol treatment studies. Trajectory analyses can better capture differences in treatment effects and may provide insight on the optimal duration of future clinical trials and grace periods. This improves on the limitation of commonly used parametric (e.g., linear) methods that cannot capture nonlinear temporal trends in the data.

Methods: We propose an exploratory approach, using more flexible smoothing mixed effects models, more accurately to characterize the temporal patterns of the drinking data. We estimated the trajectories of the treatment arms for data sets from 2 sources: a multisite topiramate study, and the Combined Pharmacotherapies (acamprosate and naltrexone) and Behavioral Interventions study.

Results: Our methods illustrate that drinking outcomes of both the topiramate and placebo arms declined over the entire course of the trial but with a greater rate of decline for the topiramate arm. By the point-wise confidence intervals, the heavy drinking probabilities for the topiramate arm might differ from those of the placebo arm as early as week 2. Furthermore, the heavy drinking probabilities of both arms seemed to stabilize at the end of the study. Overall, naltrexone was better than placebo in reducing drinking over time yet was not different from placebo for subjects receiving the combination of a brief medical management and an intensive combined behavioral intervention.

Conclusions: The estimated trajectory plots clearly showed nonlinear temporal trends of the treatment with different medications on drinking outcomes and offered more detailed interpretation of the results. This trajectory analysis approach is proposed as a valid exploratory method for evaluating efficacy in pharmacotherapy trials in alcoholism.

Figure 1

Trajectory analysis of the probability of daily heavy drinking from the Topiramate and COMBINE studies. Top-left: topiramate study; top-right: for naltrexone among subjects receiving MM and CBI in the COMBINE study; bottom-left: for naltrexone among subjects receiving MM but no CBI in the COMBINE study; bottom-right: for naltrexone among all subjects (MM only and MM plus CBI) taking pills in the COMBINE study. The open circles are the sample daily summary for the placebo group, and the solid circles are the sample daily summary for the medication (topiramate or naltrexone) group. Solid line: medication (topiramate or naltrexone) ; dashed line: placebo; dotted line: 95% confidence interval.