Controlled-Trial Designs

1. 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.

2. Posts-only Controlled Trial • Least disturbance of subjects • Large sample size, but sample size is smaller than for the usual pre-post designs for variables with sufficiently poor reliability. • Analyze via unequal-variances unpaired t. • Can get estimate of individual responses as an SD, but not usefully for individuals.

3. washout • 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.

4. 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.

5. Decision Tree

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

7. a Is the measure reliable over the intervention period? NO YES Posts - only trial n=2x 150

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

9. b Is the measure reliable 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