Case study research can be based on either a single case or multiple cases (Berg, 2001; Yin, 1993). When two or more settings are studied, they are considered to be multi-case studies (Bogdan & Biklen, 1998) or collective case studies (Stake, 1994).
Single case design is ideal for studying extreme cases, to confirm or challenge a theory or for cases where a researcher did not have access previously. Multiple cases are attempted when the purpose is to strengthen the understanding of a broader context within which a particular phenomenon is occurring (Stake, 1994) Multiple case design serves to confirm evidence which enhance the reliability and validity of a research work.