Describes the risk difference with examples. CTSpedia website provides useful tools to clinical and translational researchers.
www.ctspedia.org/
Boston University of Public Health
A comprehensive lecture note with self assessment question and tips for students.
http://sphweb.bumc.bu.edu
A PPT on Odds Ratios, Hazard Ratios, Risk Differences, Precision by Elizabeth S. Garrett from series of Clinical Trials in 20 hours
http://people.musc.edu/~elg26/talks/