How does one calculate the sample size needed for a study in which a cohort of subjects will have a single continuous variable measured at the time of a surgery and then two years later they will be classified as functional outcome or impaired outcome.
We would like to see if that measurement could have predicted the bad outcome. At some point we may want to derive a cut point in the continuous variable above which we would try to intervene to diminish the probability of the impaired outcome.
Any ideas? Any R implementation.
Best Answer
Sample size calculations for logistic regression are complex. I wont attempt to summarise it here. Reasonably accessible solutions to this problem are found in:
Hsieh FY. Sample size tables for logistic regression. Statistics in Medicine. 1989 Jul;8(7):795-802.
Hsieh FY, et al. A simple method of sample size calculation for linear and logistic regression. Statistics in Medicine. 1998 Jul 30;17(14):1623-34.
An accessible discussion of the issues with example calculations can be found in the last chapter (Section 8.5 pp 339-347) of Hosmer & Lemeshow's Applied Logistic Regression.