Blocking and Causality
Matt Bogard (noreply@blogger.com)
In a previous post I discussed block randomized designs. Duflo et al (2008) describe this in more detail: "Since the covariates to be used must be chosen in advance in order to avoid specification searching and data mining, they can be used to stratify (or block) the sample in order to improve the precision of estimates. This technique (¯rst proposed by Fisher (1926)) involves dividing the sample into groups sharing the same or similar values of certain observable characteristics. The randomizat