IDIOGRAPHIC AND NOMOTHETIC EXPLANATIONS
By focusing on a very restricted range of variables the earlier designs achieve a narrow or nomothetic explanation. That is, they achieve partial explanations of a class of cases rather than a ‘full’ explanation of a particular case. They involve an examination of fewer causal factors and a larger number of cases. For example, a nomothetic explanation might examine divorces as a class of cases and identify key factors that contribute to divorce overall (e.g. age of marriage, external family stressor etc.). The nomothetic approach contrasts with idiographic explanation. Idiographic explanation focuses on particular events, or cases, and seeks to develop a complete explanation of each case. For example, an idiographic explanation of a divorce would examine a particular divorce and develop a full picture of why that divorce occurred.
CASE STUDY DESIGNS
Case studies can be utilized for both types of explanation. A case study adopts an idiographic approachwhen a full and contextualized understanding of a case is achieved. But case study designs can adopt a nomothetic approach. This occurs when particular cases are used to achieve a more generalized understanding of broader theoretical propositions (see discussion of case studies and theory in Chapter 13). By developing a full, well-rounded causal account, case studies can achieve high internal validity. By seeing particular causal factors in combination with other causal factors we can assess both the relative importance of particular causes and the way in which various causes interrelate. As such, case studies can achieve a sophisticated and balanced account of causal processes and, in so doing, avoid mistaking cause with correlation.