A psychologist interested in the effect of a new therapy for depression recruite

Question

A psychologist interested in the effect of a new therapy for depression recruited a sample of 20 individuals who sought relief from their depression. At the beginning of the study he asked all participants to complete a questionnaire about their symptoms of depression. The mean depression score for the sample was 42 (the highest possible score is 63), indicating severe depressive symptoms. (Individuals who are not depressed typically score in the 0 to 10 range). During the next 16 weeks the psychologist treated participants in the study with a new treatment. At the end of the treatment the participants completed the depression questionnaire again. The mean score for the posttest was 12, indicating that, on average, participants’ depression symptoms were dramatically reduced and now indicated only mild depression. The psychologist concluded that the treatment was effective; that is, the treatment caused their depressive symptoms to improve. I want you think of potential threats to internal validity, and how those threats might also be responsible for the change in scores.

Explain how maturation likely plays a role in this study. How could you test if maturation was responsible for the effects here?

Explanation / Answer

The potential threats to internal validity in this study are:

Instrument change (instrumentality): The instrument used during the testing process can change the experiment. In this case, the psychologist uses a new instrument to measure the posttest score. This may have resulted in a change in the criteria he/she used to make judgments.

History: Events outside of the study/experiment or between repeated measures of the dependent variable may affect participants' responses to experimental procedures. In this case, 16 weeks were allowed to pass between the prettest and posttest condition. There is a good likelihood that the participants may have experienced several events that can impact their scores.

There is a chance that maturation may have occurred during the course of the experiment as it spanned over a duration of 16 weeks, Maturation refers to the changes that subjects undergo during the course of the experiment or even between measurements. The easiest way is to test for maturation effects is to have a control group, or group of subjects that do not get the same treatment as the main, or experimental, group that he's studying.

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