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Medical Care:
doi: 10.1097/MLR.0b013e3182984c1f
Original Articles

Group-based Trajectory Models: A New Approach to Classifying and Predicting Long-Term Medication Adherence

Franklin, Jessica M. PhD*; Shrank, William H. MD*; Pakes, Juliana MEd*; Sanfélix-Gimeno, Gabriel PhD, PharmD*,†,‡; Matlin, Olga S. PhD§; Brennan, Troyen A. MD, JD§; Choudhry, Niteesh K. MD, PhD*

Supplemental Author Material


In an article in the September 2013 issue of Medical Care, a figure printed incorrectly. The correct Figure 2 on page 792 should be:

This correction has been noted on the online version of the article, which is available at

Medical Care. 51(11):1029, November 2013.

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Classifying medication adherence is important for efficiently targeting adherence improvement interventions. The purpose of this study was to evaluate the use of a novel method, group-based trajectory models, for classifying patients by their long-term adherence.

Research Design:

We identified patients who initiated a statin between June 1, 2006 and May 30, 2007 in prescription claims from CVS Caremark and evaluated adherence over the subsequent 15 months. We compared several adherence summary measures, including proportion of days covered (PDC) and trajectory models with 2–6 groups, with the observed adherence pattern, defined by monthly indicators of full adherence (defined as having ≥24 d covered of 30). We also compared the accuracy of adherence prediction based on patient characteristics when adherence was defined by either a trajectory model or PDC.


In 264,789 statin initiators, the 6-group trajectory model summarized long-term adherence best (C=0.938), whereas PDC summarized less well (C=0.881). The accuracy of adherence predictions was similar whether adherence was classified by PDC or by trajectory model.


Trajectory models summarized adherence patterns better than traditional approaches and were similarly predicted by covariates. Group-based trajectory models may facilitate targeting of interventions and may be useful to adjust for confounding by health-seeking behavior.

Copyright © 2013 by Lippincott Williams & Wilkins


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