Contemporary Clinical Trials. 2008 Sep;29(5):705-10. Epub 2008 May 6.
Usefulness of a run-in period to reduce drop-outs in a randomized controlled trial of a behavioral intervention.
Ulmer M, Robinaugh D, Friedberg JP, Lipsitz SR, Natarajan S.
VA New York Harbor Healthcare System, New York, NY, USA.
Significance:
Since many randomized controlled trials of behavioral interventions face difficulty retaining participants, it is very important to find ways to improve retention in order to preserve study validity and maintain statistical power. Using a simple run-in period this study demonstrates a successful way to decrease drop-outs. When such an approach is used: a) more complete data and more equal distribution of participants across the arms of a study is probable, b) differences found when analyzing the results are more likely due to differences in treatment, since the completers in each of the study arms are more similar, thus minimizing the possibility that differences are due to confounders or differences in the number of participants, and c) a greater percentage of those randomized actually receive the assigned treatment, and when intent-to-treat analyses are performed, typically larger differences between the study arms (higher power) is noted than when no run-in period is used.
Abstract:
OBJECTIVES: We evaluated the usefulness of a simple run-in period to reduce drop-outs in a behavioral intervention to improve blood pressure (BP). In a pilot study where a run-in period was not used, we had a 25% drop-out rate.
METHODS: A prospective evaluation was performed in the context of a blinded 3-arm randomized trial. Participants are eligible if they have uncontrolled BP on 2 consecutive visits. Potential participants are approached during a routine visit, informed, consented and enrolled. After a 1-month run-in period during which all participants receive a phone call to: i) verify phone availability, ii) get basic information on treatment, and iii) confirm the baseline visit, participants return for a baseline visit. They are then randomized to one of the three treatment arms: usual care, non-tailored counseling, or tailored counseling. Participants make return visits at 3, 6 and 12 months.
RESULTS: Of the 1275 potential participants who received detailed study information, 301 consented to participate, of whom 226 were enrolled. During the run-in period, 73 withdrew consent and 153 participants were randomized; 7 subsequently dropped out. There were no differences (p>.1) between the 73 cancelled and the 153 randomized patients. There were fewer drop-outs than in the pilot study (5% vs. 25%, p<.0001).
CONCLUSIONS: The run-in period reduces the number of drop-outs after randomization and improves statistical power. In order to retain external validity, it is important to compare participants who remain in the study and those that cancel, and incorporate that in generalizing from the study.
