In the Causality post, I discussed the Solomon four group design. This design addressed some concerns on internal and external validity.
In this post, I will discuss other research designs, their advantages and disadvantages.
Nonequivalent Control Group Design
- Controls for the main effects of history, maturation, testing, instrumentation, selection and maturation.
- We do not test for the interaction between selection and maturation.
- The problem of regression.
- This design has internal validity on all the individual points.
- There are systematic selection factors involved in the natural assemblage of the groups, as well as the effects associated with specific sequences of treatments.
- An extended version of the Time Series design and the Nonequivalent Control Group design, this model controls for all internal sources of validity.
- The only disadvantage is that we are not controlling for potential interaction of testing and selection with X.
- Maturation is well controlled for (unless it is very abrupt), instrumentation is also well controlled for assuming we keep the same measures.
- Regression, selection and mortality effects may also be ruled out.
- Failure to control history is the biggest weakness.