1. Construct validity: refers to the adequacy (or the quality) of the definitions of both the IV and the DV used in the study.
 

2. External validity: the degree to which research findings generalize beyond the specific context of the study.

a. generalizing to other people

b. generalizing to other environments

c. generalizing to other times

3. Internal validity: the degree to which an experiment is designed well methodologically and is free of confounding variables.
 

4. Pre-Post Studies

a. History and maturation

b. Testing and instrumentation

5. Subject problems

a. Subject selection

b. Attrition