Hey guys, I need some help calculating the minimum sample size needed for my upcoming trial. I’m doing higher degree research on eHealth, so I have little knowledge about statistics and sample size calculation. Was doing loads of research online and trying out online calculators but I’m still not too sure.

So basically I’ve done an initial trial on a small sample of 24 participants, randomly allocated to two groups (13 in control group and 11 in intervention group), the aim is to see whether the use of an IT based intervention can improve health supplement adherence rate when compared to a control group using a pillbox. Below is the result from the initial trial:

Control group- average baseline adherence rate before trial was 86%, and after trial the average adherence rate increased to 95%

Intervention group- average baseline adherence rate before trial was 81%, and after trial the average adherence rate increased to 98%

So what I would like to know is: what is the minimum number of participants I will need for each group (I want a 2:1 ratio, so more people in the intervention group). I need to know the very minimum number as I was having problem recruiting enough participants in the initial trial, and I’m currently starting the recruitment process for the upcoming full trial. I plan to recruit about 40 people in intervention and 20 in control, is this enough?

Power=at least 80%, and alpha=0.05

I’ve tried this online calculator, but unsure what to put in the anticipated incidence sections, or if it is the right calculator to use in my case: https://clincalc.com/stats/samplesize.aspx

Any help will be appreciated.