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.

How might testing effects impact the scores? How might you deal with this issue?

Explanation / Answer

Threats to Internal validity can be loosely categorised into one of three types: threats relating to the passage of time, threats relating to selection of participants, and threats relating to testing and manipulations.

Now, we will deal with each threats one by one briefly.

Threats Relating Passage of time

Threats relating to the passage of time are a potential problem whenever a repeated measures design is employed. There are five main threats in this category: maturation, history, mortality, instrumentation and statistical regression to the mean.

Maturation-This threat concerns changes within participants due to the passage of time, such as developmental changes, aging, hunger, fatigue etc.For example if the project lasts a long period of time, most participants may improve their performance regardless of treatment.

History-History refers to events occurring between pre- and post-test in addition to the experimental manipulation that can influence the dependent variable. Whilst maturation effects are events happening within participants, history effects are events happening to participants.

Mortality-The threat of mortality is concerned with dropouts from a study between pre- and post-test.Dropouts may be systematically different from participants who remain in a study.

Instrument-It is a problem when the way in which the dependent variable is measured varies from pre-test to post-test or between different groups. This may be due to calibration errors in an instrument, the use of different instruments, or by experimenters using the instruments in different ways.

Statistical Regression to Mean-This is a complex statistical phenomenon that can occur in pre-test and post-test designs. Whenever we take a pre-test measure, some people will happen to score low or high on the variable due to some factor that will not be present at post-test. Then when you take the post-test measure, those people will not score so low or high again.

Threats Relating to Selection of Participants

These threats are concerned with biases introduced in assigning participants to treatment conditions in multiple group studies.

Threats Relating to Testing and Manipulations-

These are threats concerned with the act of testing participants and with potential effects of the manipulation other than those that are intended.

Testing- Threats relating to Testing concerned with the effects of taking a test on the outcomes of taking a second test. In other words, the pre-test becomes a form of "treatment."

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.