Identifying Confounding Variables

Identify any confounding variable(s) in the following studies and comment about whether the sample is representative of the population of interest. Look for confounding variables that are obviously present in the study.

A. You are studying the effects of “pep talks” on performance. You randomly select 50 undergraduates from the college’s enrollment records; all 50 agree to participate. The first 25 students who come through the door are sent to the gym, where they are given a brief pep talk. The next 25 students who come through the door are sent to the concert hall, where they receive a dry lecture (a “fake” treatment). You record the number of errors on a simple task and compare the number of errors between groups. (So, the IV is the type of talk presented and the DV is the number of errors on a task.) You find that the pep talk group makes fewer errors.

D. You want to know whether child abuse is increasing in the US, particularly among upper middle class individuals. You call all pediatricians in your home city (all 25 of them). 10 return your calls; you ask them whether child abuse rates have increased over the past 10 years.
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Confounding variables

If a treatment is manipulating more than a variable it is stated to be a confounding variable. In a more formal definition, Mitchell and Jolley (2005) define confounding variables as “variables that are manipulated along with the treatment” (p.300). Confounding variables make it known whether the treatment had an effect. In any experiment there may be variables that confound the results (because of an error). These variables may not have not been measured and may vary within …