Controlled-Trial Designs See Batterham and Hopkins, Sportscience 9, 33-39, 2005. Choice determined by availability of subjects, reliability of dependent variable, and time to wash out treatment. Time Series Weakest design Any change post treatment could be coincidental. Analyze using within-subject modeling Fit line or curve to each subject's baseline. Extrapolate to the post-test. Paired t of observed post minus predicted post.

Posts-only Controlled Trial Least disturbance of subjects But large sample size. Analyze via unequal-variances unpaired t. Can get estimate of individual responses as an SD, but not usefully for individuals.

Pre-post Controlled Trial (or fully-controlled trial) Most common design. Analyze difference of changes via unequal-variances unpaired t. Pre-post Crossover Best design if all subjects motivated to know effect of treatment on themselves. Analyze change of changes via paired t. washout

Posts-only Crossover Least number of subjects and tests when reliability high. But can get estimate of individual responses only if include a repeat of one of the treatments for each subject. Analyze via paired t. Important to control for the order effect, if it is substantial and there are unequal numbers in the crossover groups. A spreadsheet is on its way. washout

Decision Tree

Can you use a control group or a separate control treatment? NO YES Time-series trial n=10-???

Can you do a pretest? NO YES Posts - only trial n=2x 150

Will the intervention wash out in an acceptable time for a crossover? NO YES Fully - controlled trial n=2x 10-300 -

washout+intervention period? Is the measure reliable b over washout+intervention period? NO YES Are you limited by subjects or resources? NO YES Fully - controlled Simple crossover crossover n=10-300 n=10-75