Say we are studying the effect of strict attendance policies on class participation. In our case, we saw that class participation did increase after the policy was established. There are four types of validity commonly examined in social research. Construct validity is the hardest to understand in my opinion. Overall, we are trying to generalize our conceptualized treatment and outcomes to broader constructs of the same concepts.
External validity refers to our ability to generalize the results of our study to other settings.
There are three main types of threats to internal validity - single group, multiple group and social interaction threats. Single Group Threats apply when you are studying a single group receiving a program or treatment. Thus, all of these threats can be greatly reduced by adding a control group that is comparable to your program group to your study. In our earlier example, this would mean that the stricter attendance policy did not cause an increase in class participation, but rather, the expulsion of several students due to low participation from school impacted your program group such that they increased their participation as a result. A Maturation Threat to internal validity occurs when standard events over the course of time cause your outcome.