Intention to treat analysis and estimating loss to follow up

#1
Hi guys,

Doing my MSc in Clinical Trials and after looking at a research paper I am stumped about something...

The authors have stated that the sample size needed for a detection of the primary outcome measure was 36 per group (parallel RCT) assuming a loss to follow up of 15%, with a 2 tailed α of 0.05 and a β of 0.2.
The true loss to follow up was actually 35%... They used intention to treat analysis..
Does this now make the study underpowered.. Although the original recruitment number was reached and all participants are being included in analysis??

Quite new to this and would love the help :)
Thank you so much :)
 
#2
ITT takes all subjects that were randomized. However, if subjects are lost to follow-up, you may have missing values of the primary endpoint. From now on it depends on how you handle missing values. Basically, if you need n subjects to get your power, and you have less, for whatever reason, you are under-powered.
 

hlsmith

Omega Contributor
#3
Side note, the sample size is based on a conjectured effect size. If for some reason the conjecture effect was smaller than the truth, then the study may be underpiwered for the hypothesis but still reveals statisticallly significant results (differences) .

Also, the study needs to have nondifferential loss to be unbiased.