An educational psychologist is asked to conduct a study to determine if class size has an effect on academic achievement. The psychologist identifies a large fifth-grade classroom in one inner-city school and a small fifth-grade classroom in another inner-city school. Principals from each school agree to participate in the study and select the teachers and classes. At the end of the school year, the researcher obtains achievement test scores from students in both schools and compares the mean achievements of the two groups.
Based solely on the preceding description, this job names threats to internal or external validity exist in this study and an alternative method that would strengthen the internal and external validity of this study.
The Internal Validity determines the answer to the question of whether the connection between the independent and dependent variables is a clear causality, with no confusion or ambiguity of other factors. "Is the connection between the independent variable and dependent variable clear and unambiguous to make a causal inference?" (Leman, 1991). In other words, is the independent variable really responsible for the results of the dependent ...
Validity scenarios are presented.