The association between medication usage and dropout status among participants of an exercise study for people with...

Little is known about predictors of dropout status in exercise studies for people with osteoarthritis. Losses to follow-up can pose serious threats to study validity. The purpose of this study was to assess the ability of arthritis medication usage the month prior to enrollment to predict dropout status among participants in an exercise study for people with osteoarthritis.

Men and women who participated in an exercise study for people with osteoarthritis (N=143) were followed. Participants who completed 24+ months of the exercise program were considered retained, whereas individuals who withdrew prior to 24 months were considered dropouts.

Of the 143 participants analyzed, 78 (55%) completed 24+ months of the exercise program and 65 (45%) dropped out. Among those who reported arthritis medication usage, 54% were lost to follow-up. The group reporting no usage of arthritis medication had a 20% dropout rate (odds ratio=3.5, 95% confidence interval=1.6-7.6). The final adjusted model controlling for baseline health status, body mass index, and the interaction between baseline health status and body mass index indicated that those individuals who reported arthritis medication usage were more than 4 times more likely to drop out than were those who reported no arthritis medication usage (odds ratio=4.5, 95% confidence interval=1.8-11.4).

The results showed that self-reported arthritis medication usage the month prior to study enrollment was associated with subsequent dropout status among this group of exercisers with osteoarthritis. Further identification of baseline characteristics predictive of participant dropout status may benefit future exercise studies. A priori knowledge of "at-risk" exercise study participants will afford the opportunity for the timely allocation of appropriate resources aimed at reducing losses to follow-up.