A study on a new depression treatment recruited patients who scored in the highe

Question

A study on a new depression treatment recruited patients who scored in the highest depression range ("severely depressed") on the PHQ9 depression screen questionnaire. These patients were assigned to either a treatment or a comparison group. At the end of the study the participants retook the PHQ9, and it was observed that the scores improved in both study groups. This is probably an example of:

       . A. A Reliability Threat

       . B. Regression Threat

       . C. Instrumentation Threat

       . D. A Threat to External Validity

Explanation / Answer

Option D is correct

Explanation:

When participants or subjects are selected in a manner that increases the probability of obtaining a biased sample. A threat to external validity that occurs when the selection process produces a sample with characteristics that are different from those in the population

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