Quality of case study design

Yin (2009, p.40) identifies four, widely-used tests for judging the quality of research design:

• “Construct validity: identifying correct operational measures for the concepts being studied;
  
• Internal validity (for explanatory or causal studies only and not for descriptive or exploratory studies): seeking to establish a causal relationship, whereby certain conditions are believed to lead to other conditions, as distinguished from spurious relationships;
  
• External validity: defining the domain to which a study’s findings can be generalized;
  
• Reliability: demonstrating that the operations of a study – such as the data collection procedures – can be repeated, with the same results.“

In the figure below he summarises, for a case study, what tactics are appropriate for each test and the phase of research in which the tactic applies.