<prompt> Translate the following text to EnglishKwa ajili ya masomo ya kesi hasa, lazima kuwe na msingi wa majaribio kwa ajili ya mfano uteuzi na uhakika wa homogeneity ya kutosha ya idadi ya watu.  <response>: For case studies in particular, there must be an empirical basis for instance selection and assurance of adequate population homogeneity. 