Causal-Comparative Research Designs
http://www.tsum.edu/~trenckly/week3.htm
This site is part of the web site of Tom Renckly's online research methods course. There is a very good discussion of the following aspects of causal-comparative designs: purpose, identification, limitations, evaluation, as well as the evaluation of a causal-comparative journal article.
Research Approaches
http://edweb.sdsu.edu/Courses/ED690DR/Class01/ResearchTypes.html
A short paper that offers a good comparison between several types of research designs.
