Research Design
In Social Research
David A. de Vaus
Issues in case study Design
All research design should be internally valid and externally valid, should produce reliable results and should be amenable to replication. Case study designs are often seen to be deficient in all these areas. However, careful attention to these matters at the design stage can deal with many of these criticisms.
Methodological issues
Internal validity
The internal validity of many of the research designs examined in Parts IIto IV this book depends on having groups that are comparable except in relation to specific key variables. Internal validity in these earlier designs relies on screening out the influence of variables other than the key causal variables. They involve focusing on a small number of variables and removing the influence of other variables by controls of one sort or another. Threats to internal validity stem from the danger that factors other than our key variable are producing any changes we observe.