Validity Issues

Threats to Internal validity

Internal validity is the confidence that results are from the experimental treatment and not from external factors

History Threat - Results are caused by external factors (extraneous or historical) instead of the experimental treatment or intervention.

Maturation Threat - Results are caused by maturation of subjects instead of experimental treatment or intervention.

Mortality Threats - The possibility that subjects are dropping out of control group or experimental group at different rates, skewing the end result.

Regression Threat - The groups overall end results of the post-test will regress towards the mean due to high results on the pre-test.

Instrumentation Threat - In pre-post designs, the results come from a differing degree of difficulty in the post-test instead of from the intervention itself.

Testing Threat - In pre-post designs, if participants remember their answers from the pre-test it may affect their answers on the post-test.

(Bhattacherjee, 2012; Dimitrov & Rumrill, 2003; Engel & Schutt, 2014)

Improving Validity:

Manipulation - The manipulation of the independent variable so that it is only received by the treatment group.

Randomization - Treatment and control groups are randomly assigned from the sample of participants.

Controls - Eliminating or including factors from the environment that can potentially affect/alter outcomes

(Engel & Schutt, 2014)