Discussion:
Threats to internal or external validity
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.