One widely known method of correcting for selection effects by creating equivalent groups in quasi- or non-experimental studies is propensity score matching (Rubin, 1997). In matching methods, generally, a non-experimental control group is constructed, either from a supplemental dataset or (in a quasi-experiment) from a non-randomized control sample. This constructed control group is designed to be equivalent to the treatment group, which is accomplished through matching observations from the supplementary sample to those in the treatment sample on a set of explanatory variables presumed to be relevant to the outcome. Criteria used to create a matched group differ in various matching me
Washington State Institute for Public Policy has published a second update of its 2004 report, " Benefits and Costs of Prevention and Early Intervention Programs for Youth" (Steve Aos, Roxanne Lieb, Jim Mayfield, Marna Miller, Annie Pennucci. WSIPP #04-07-3901). The new report, " Return on Investment: Evidence-Based Options to Improve Statewide Outcomes April 2012 Update" (Stephanie Lee, Steve Aos, Elizabeth Drake, Annie Pennucci, Marna Miller, Laurie Anderson. WSIPP #12-04-1201) is available here.
