Resources for handling blocked randomization in the analysis of RCTs

This happens to me too. What is the difference between “stratifying” vs “blocking” for specific covariates in an RCT? As far as I can tell, people use the two interchangeably but “stratification” comes from sampling theory whereas “blocking” comes from experimental design.

Thus, “stratification” implies a procedure that almost never happens in RCTs, i.e., that patients were sampled from a population based on a stratification factor such as age. Instead, enrolled patients (typically a convenience sample) are randomized within blocks based on specific blocking factors such as age. It is even more preferable to covariate adjust for the blocking factor.

Related discussion with @ChristopherTong and @ESMD on the differences between random sampling and random allocation.

2 Likes