    Sentence 1: Usually, sites for program effects  case studies should be selected with great care  for criteria such as whether there is evidence  that the program has been implemented at the  site, whether the site has been subjected to  changes that could have the same effects as  ithe program or that ‘tould mask its effects, and  how the addition of this site to the group of  sites being d supports the  generalizability of the findings.           Sentengp 2: There  sites fo programs.         no criteria for selecting    