         Sentence 1: Usually, sites for program eltects case  Studies should be Selected with great care tor 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  etfects a5 the program or that could mask its effects,  and how the addition of this site to the group of sites  being ‘suidied supports the serait of the  findings.    ‘Sentence 2: The addition of a site:Mpan existing group  Of sites under study has to support generalizability of  the findings.