THREATS TO VALIDITY

How effective are the Educational Programs and Instructional Language Strategies for Improving the LEP Learners' Standardized Scores?

How effective are the Educational Programs and Instructional Language Strategies for Improving the LEP Learners' Standardized Scores?

Validity is the strength of our conclusions, inferences or propositions. More formally, Cook and Campbell (1979) define it as the "best available approximation to the truth or falsity of a given inference, proposition or conclusion." In short, were we right? Let's look at a simple example. 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. Each type of validity would highlight a different aspect of the relationship between our treatment (strict attendance policy) and our observed outcome (increased class participation).

Threats To Internal Validity

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.

A History Threat occurs when an historical event affects your program group such that it causes the outcome you observe (rather than your treatment being the cause). 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. For example, if by chance, the students who participated in your study on class participation all "grew up" naturally and realized that class participation increased their learning (how likely is that?) - that could be the cause of your increased participation, not the stricter attendance policy.

A Testing Threat to internal validity is simply when the act of taking a pre-test affects how that group does on the post-test. For example, if in your study of class participation, you measured class participation prior to implementing your new attendance policy, and students became forewarned that there was about to be an emphasis on participation, they may increase it simply as a result of involvement in the pretest measure - and ...