Outcome Assessment and Sample Size Requirements

Background and Purpose: The purpose of this study was to analyze recovery of motor function in a cohort of patients presenting with an acute occlusion in the carotid distribution. Analysis of recovery patterns is important for estimating patient care needs, establishing therapeutic plans, and estimating sample sizes for clinical intervention trials. Methods: We prospectively measured the motor deficits of 104 stroke patients over a 6-month period to identify earliest measures that would predict subsequent motor recovery. Motor function was measured with the Fugl-Meyer Assessment. Fifty-four patients were randomly assigned to a training set for model development; SO patients were assigned to a test set for model validation. In a second analysis, patients were stratified on basis of time and stroke severity. The sample size required to detect a 50% improvement in residual motor function was calculated for each level of impairment and at three points in time. Results: At baseline the initial Fugl-Meyer motor scores accounted for only half the variance in 6-month motor function (r=0.53,/><0.001). After 5 days, both the 5-day motor and sensory scores explained 74% of the variance (/><0.001). After 30 days, the 30-day motor score explained 86% of the variance (p<0.001). Application of these best models to the test set confirmed the results obtained with the training set. Sample-size calculations revealed that as severity and time since stroke increased, sample sizes required to detect a 50% improvement in residual motor deficits decreased. Conclusions: Most of the variability in motor recovery can be explained by 30 days after stroke. These findings have important implications for clinical practice and research. (Stroke 1992;23:1084-1089)