Question

A physical education teacher uses a nonequivalent pretest-posttest experimental control group design to test the effectiveness of a new exercise routine on student flexibility with four classes of tenth graders. What are the threats and justifications to internal and external validity?

Answer 1

For many true experimental designs, pretest-posttest designs are the preferred method to compare participant groups and measure the degree of change occurring as a result of treatments or interventions.

Internal validity refers specifically to whether an experimental treatment/condition makes a difference or not, and whether there is sufficient evidence to support the claim.

External validity refers to the generalizability of the treatment/condition outcomes.

The factors of internal validity -

History, Maturation, Testing, Instrumentation, Statistical regression, Selection of subjects, Experimental mortality, Selection-maturation interaction,

Factors of external validity-

Reactive or interaction effect of testing, Interaction effects of selection biases and the experimental variable, Reactive effects of experimental arrangements, Multiple treatment interference