Methods in Behavioral Research by Paul Cozby & Scott Bates

Author:Paul Cozby & Scott Bates [Cozby, Paul & Bates, Scott]
Format: epub
Tags: Psychology, Experimental Psychology
ISBN: 9780078035159
Google: puKkuQAACAAJ
Published: 0101-01-01T00:00:00+00:00

LEARNING OBJECTIVES

▪ Provide a definition of a confounding variable and describe how confounding variables are related to internal validity.

▪ Describe the posttest-only design and the pretest-posttest design, including the advantages and disadvantages of each design.

▪ Contrast an independent groups design with a repeated measures design.

▪ Summarize the advantages and disadvantages of using a repeated measures design. Explain how counterbalancing provides a way of addressing the order effects problem.

▪ Describe a matched pairs design, including reasons to use this design.

IN THE EXPERIMENTAL METHOD, THE RESEARCHER ATTEMPTS TO CONTROL ALL EXTRANEOUS VARIABLES. Suppose you want to test the hypothesis that exercise affects mood. To do this, you might put one group of people through a 1-hour aerobics workout and put another group in a room where they are asked to watch a video of people exercising for an hour. All participants would then complete the same mood assessment. Now suppose that the people in the aerobics class rate themselves as happier than those in the video-viewing condition. Can the difference in mood be attributed to the difference in the exercise? Yes, if there is no other difference between the groups. However, what if the aerobics group was given the mood assessment in a room with windows but the video-only group was tested in a room without windows? In that case, it would be impossible to know whether the better mood of the participants in the aerobics group was due to the exercise or to the presence of windows.

CONFOUNDING AND INTERNAL VALIDITY

Recall from the chapter “Fundamental Research Issues” that the experimental method has the advantage of allowing a relatively unambiguous interpretation of results. To conduct a true experiment, the researcher manipulates the independent variable to create groups. All other variables are kept constant, either through experimental control or through randomization including random assignment to groups. The groups are then compared on the dependent variable. If the groups are different, the researcher can conclude that the independent variable caused the results, because the only difference between the groups is the manipulated variable.

Although the task of designing an experiment is logically elegant and exquisitely simple, you should be aware of possible pitfalls. In the hypothetical exercise experiment just described, the variables of exercise and window presence are confounded. The window variable was not kept constant. A confounding variable is a variable that varies along with the independent variable. Confounding occurs when the effects of the independent variable and an uncontrolled variable are intertwined so you cannot determine which of the variables is responsible for the observed effect on the dependent variable. If the window variable had been held constant, both the exercise and the video condition would have taken place in identical rooms. That way, the effect of windows would not be a factor to consider when interpreting the difference between the groups.

In short, both rooms in the exercise experiment should have had windows or both should have been windowless. Because one room had windows and one room did not, any difference in the dependent variable cannot be attributed solely to the independent variable.

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