improve your relationship?
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Professor James McNulty, a social psychologist who studies relationships, was asked by the Department of Defense to develop an intervention to help couples cope with the separation of a deployment. How can couples stay close when their partner is far away for months at a time?
McNulty and his team of students tested an intervention in which couples viewed photos of their partner placed next to cute images of puppies, kittens, or baby bunnies. Would just seeing your spouse next to cuteness make you feel closer to your spouse? Here's how a journalist from National Geographic described the study:
For six weeks, one group of partners was shown a stream of images every three days that repeatedly paired their partner's image with that of a positive image, like a puppy. The control group saw pictures of their partners paired with neutral images, such as a shirt button.
Every two weeks [beginning at the start of the study], the couples' attitude toward each other were measured by the positive and negative words used when reviewing a series of faces, of which their partner was included. When couples were evaluated at the end of the study, those who had been shown positive images had more positive associations with their partners and improved marriage quality.
There were 144 couples in the study. You can read the empirical journal article here, in the journal Psychological Science.
Questions.
a) McNulty and his team conducted an experiment. What are the independent and dependent variables? Was the independent variable manipulated as within groups or independent groups?
b) Which type of experiment does it appear to be, based on the description: Posttest-only? Pretest-posttest? Concurrent measures? Repeated measures?
c) Think about the design of this study and consider the 12 internal validity threats presented in Table 11.1. Which threats can you probably rule out, given the design of this study? Which threats do you think might still be in question? What questions might you ask about the study to assess these remaining threats to internal validity?
Suggested answers:
a) The independent variable was which type of treatment they were in: Pairing their partner's face with cute animals or with neutral objects. This was an independent groups IV. The dependent variables included the positive and negative emotions people felt, and their marriage quality. That is, there were multiple dependent variables in the study.
b) This appears to be an independent groups design; specifically, a prettest-posttest design.
c) The researchers randomly assigned couples to the two groups, so we can rule out selection effects. It's not a repeated measures design, so we don't need to worry about order effects. Because they used a control group and an experimental group, we can rule out threats such as maturation, testing, regression, instrumentation, and history, because these threats would have applied equally to both experimental and control groups and thus evened out. We might ask about attrition (selection-attrition) in the two groups in case the unhappiest couples dropped out of the experimental group more often (however, if attrition was similar in the two groups then attrition is not an internal validity threat). We might wonder if some couples guessed the hypothesis of the study and changed their answers (experimental demand). Since both groups received a treatment (either the cute photos or the neutral photos), we can probably rule out a placebo effect. The dependent measures appear to be self-report, so observer bias is unlikely here.