Study staff are working with a national sampling firm to recruit subjects and obtain 400 responses. Subjects were randomly assigned to one of four arms. (1) Colorectal cancer screening good shared decision making video then poor video second (2) Colorectal cancer screening poor shared decision making video then good video (3) Treatment of high cholesterol good video then poor video and (4) Treatment of high cholesterol poor shared decision making video first then good video. Participants completed measures of Shared Decision Making after each video.
The sample size was determined to ensure sufficient power to detect differences between the good and the poor shared decision making videos in this repeated measure design and analyses were planned to be separate for each arm (i.e. one analysis for the colorectal cancer screening videos and a separate parallel analysis of the statins for high cholesterol video). To detect an eta2 effect size of .04 with an alpha of 0.05 with 80% power would require 190 observations per clinical condition. Study staff rounded this to 200 observations per clinical condition, for a total required sample size of 400 patients.
The interventions were short Shared Decision Making Videos that were developed as part of two training courses on shared decision making by investigators at Massachusetts General Hospital.
For the analyses, study staff will examine the descriptives of the Shared Decision Making Process items for the two clinical conditions and orders. Study staff will examine rates of missing data to determine acceptability, and will examine descriptive results to see whether the scores span the range of total possible scores, are normally distributed, and whether there is evidence of floor or ceiling effects. Then, study staff examine discriminant validity of the measure by examining whether scores for the good videos are higher then for the poor videos. Further, study staff will examine concurrent validity with the alternative shared decision making measure.
