powersim_workshop_2026/04_ancova/exercises-ancova1.md

Exercise: Analysis and power simulation for baseline/follow-up measurements

Shoulder pain and acupuncture

1. Reanalyze the original data
   • Re-estimate the ANCOVA model for the Kleinhenz et al. (1999) data
2. Run a power simulation for a replication study
   1. Draw plausible pre-CMS values
   2. Specify the minimum relevant average treatment effect (ATE)
   3. Set the remaining parameters to plausible values
   4. What is the sample size required for the test to detect the effect with 80% power?
   5. How robust is the power simulation when you repeat it with a new set of pre-CMS values? Try it!
   6. Recover the parameters of the ANCOVA model

References

Kleinhenz, J., K. Streitberger, J. Windeler, A. Güßbacher, G. Mavridis, and E. Martin. 1999. “Randomised Clinical Trial Comparing the Effects of Acupuncture and a Newly Designed Placebo Needle in Rotator Cuff Tendinitis.” Pain 83 (2): 235–41.