Ex Post Facto Designs
http://plato.acadiau.ca/COURSES/PSYC/McLeod/2023Research/ex-post.htm
This is a brief introduction to ex post facto designs and the critical issues related to them.
Chapter 16: Causal Comparative Research
http://www.mhhe.com/socscience/education/fw/sg/olc/16major.htm
This is a good bulleted list of the issues related to causal-comparative research.
