You have several ways to estimate the required sample size. The most general and most

accurate way is to use power/sample-size software such as G*Power, which is described in

detail in Chapter 4. Or you can use the online sample-size calculator at

https://clincalc.com/stats/samplesize.aspx, which produces the same results.

You need to enroll additional subjects to allow for possible attrition during the study. If you

expect x percent of the subjects to drop out, your enrollment should be:

So, if you expect 15 percent of enrolled subjects to drop out and therefore be unanalyzable, you need

to enroll 100 × 197/(100 – 15), or about 231 participants.