Types of case studies and implemending triangulation in them

In the current era, as other areas of social research methods, transition has occurred. Moving the social research methods from quantitative and strict methods to qualitative, humanistic and interpretive ones have doubled the importance of qualitative social researches.  The case study is also one of the most common methods of qualitative research which examines the unique form of a single case such as a person, family, community etc. In this method, according to Leen, phenomena within the context of real life are studied in integrated form through the inductive approach and with the aim of theory building.As one of the criticisms on case study method is its low internal validity, so this study tries to explain the case study and its different types (intrinsic, instrumental and original), and using the triangulation in case studies in order to validate research findings and case studies (construct validity of case study). As the main function of the triangulation is using the different methods in order to decrease the level of misinterpretation, improve the internal validity and also converge the different perspectives, we hope that using it in qualitative methods, especially in case study helps us to overcome this problem.