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Discussion: Confounding Variables

Internal validity in a research study is the extent to which changes in the dependent variable can confidently be attributed to the influence of the independent variable rather than to possible confounding variables. In other words, was it really the independent variable that had an effect on the dependent variable or did something else cause the effect?

For example, presume that an instructor wants to try a new reading efficiency strategy to improve reading comprehension of college students in an online course. The instructor divides the class into two equal groups. One group (the experimental group) reads a passage using the new reading strategy taught by the instructor. The other group (the control group) reads the same passage but is not exposed to the new strategy. Next, both groups of students complete a reading comprehension test. The assumption is that if the group exposed to the new reading strategy scored higher than the other group, the new reading strategy is effective.

What else could explain the difference in scores? Is it possible that the students enrolled in the group that learned the new strategy already had high reading comprehension skills? What if this group already knew more about the information in the reading passage? Could the instructor have inadvertently biased the study because he taught the new reading strategy, and he selected the reading passages that both groups read?

Possible situations, or reasons, that could interfere with obtaining accurate results are called confounds, and could be a threat to the internal validity of a study. It is important to keep in mind though, that the presence of a possible confounding variable in a study does not necessarily mean it is responsible for obtained results. Rather, the independent variable (e.g., the reading intervention) may have actually had an effect on the dependent variable (the test results).

In this Discussion, you will examine possible confounding variable(s) in research studies from your course textbook and apply methodology for addressing and/or eliminating the possible confound(s).

To prepare:

• Read Chapter 12 in your course text.
• Read the “Thinking Critically About Research” scenarios (a—i) in Chapter 12, pages 256–258.
• Choose the scenario that most interests you. Note: Before selecting a scenario, view the Discussion 4 Forum to see if any colleagues have already posted. If so, select a letter that has not yet been chosen. All nine (a–i) letters should addressed before a student repeats a letter.

For your chosen scenario, determine the possible confounding variable(s) (there may be more than one), and consider how they might be eliminated using research designs presented in the readings (e.g., 2×2 factorial design).

Note: You can assume that random assignment took care of any potential differences in the groups; therefore, group differences are not a potential confound.

With these thoughts in mind:

By Day 3

1. Indicate the letter of the scenario you selected in the “Subject” field of your post. You should be addressing a scenario different from those posted, unless your colleagues have already addressed all nine scenarios. Identify and explain the possible confounding variable(s) (e.g., demand characteristics, placebo effect) in your chosen scenario.
2. Drawing from the Learning Resources this week, explain a specific research design (e.g., 2×2 factorial design, repeated measures design) the researcher(s) could use to control for confounding variables.

Note: Be sure to support the responses within your Discussion post, and in your colleague reply, with evidence from the assigned Learning Resources.