2. A researcher uses a simple between-subjects experiment involving 10 participants to examine the effects of memory strategy (repetition versus imagery) on memory.
a. Do you think the researcher will find a significant effect? Why or why not?
No—too few participants to have any power.
b. What design would you recommend?
A counterbalanced design so that the researcher could have the power of a within-subjects design and yet control for order effects.
c. If the researcher had used a matched pairs study involving 10 participants, would the study have more power? Why?
Yes—the design should have more power because random error due to individual differences would be reduced, thereby making the treatment effect easier to detect.
Only 4 (one less than the number of pairs).
What type of matching task would you suggest? Why?
A reliable, sensitive, valid memory test that would be similar to the memory test used in the real study. Ideally, we would use a test that correlated highly with the real measure.
We would use such a task because we do not have to worry about deception and because it is most likely to give us accurately matched pairs (a real concern when we only have five pairs).
4. What problems would there be in using a within-subjects design to study the “humor-perseverance” study discussed in question 3?
Participants would probably figure out what the study was about, thus hurting construct validity. Also, participants might be more frustrated during the second exposure to the frustrating task (a practice effect). In addition, there might be an interesting carry-over effect of humor for participants receiving the humor/no-humor sequence: Irritability in the “no humor” condition might be due to “coming down” from laughing (if one buys opponent process theory).
Would a counterbalanced design solve these problems?
Not completely. However, it might be able to balance out and measure these effects. Thus, the design might let you know that these factors were problems.
6. Two researchers hypothesize that spatial problems will be solved more quickly when the problems are presented to participant’s left visual fields than when stimuli are presented to participant’s right visual fields (because messages seen in the left visual field go directly to the right brain which is often assumed to be better at processing spatial information). Conversely, they believe verbal tasks will be performed more quickly when stimuli are presented to participants’ right visual fields than when the tasks are presented to participants’ left visual fields. What design would you recommend? Why?
A within subject design or a counterbalanced design because the differences looked for are probably fractions of seconds, so you need a powerful design that will reduce error variance and allow you to get many observations. The hypothesis is not so intuitive that participants are likely to guess it and play along. Therefore, sensitization is not a big problem. A few warm-up trials could minimize practice effects and keeping the study short would minimize fatigue effects (especially since the task is so simple). In addition, we could use counterbalancing to balance out practice and fatigue effects.
8. You want to determine whether caffeine, a snack, or a brief walk has a more beneficial effect on mood? What design would you use? Why? How?
A between-subjects design would probably be best to avoid problems with (a) the order effects that would affect within subject designs and (b) catching on to the hypothesis (sensitization) that would affect both matched pairs and within subject designs. This would be done simply by randomly assigning participants to groups. If you did not want to use a pure between-subjects design, you could use a mixed design in which the within-subjects variable would be before vs. after the treatment and the between-subjects variable would be caffeine vs. snack vs. the brief walk. In that case, you would be looking for a significant interaction between trials (before or after) and the treatment variable.
10. A researcher wants to know whether music lessons increase scores on IQ subtests and whether music lessons have more of an effect on some subtests (e.g., more of an effect on math than on vocabulary) than others.
a. Would you make music lessons a between or within subjects factor? Why?
Between-subjects. It varies between-subjects in real life and there might be substantial carryover effects.
b. Would you make subtests a between or within subjects factor? Why?
A within-subjects factor. There is little concern about order effects and it would give the study much more power.
c. If the researcher did an analysis of variance (ANOVA) on the data, the researcher would obtain three effects. Name those three effects.
A between-subjects main effect for music lessons, a within-subjects main effect for subtests, and an interaction between subtests and music lessons.
d. What effect would the researcher look for to determine whether music lessons increase scores on IQ subtests
The between-subjects main effect of music lessons.
e. What effect would the researcher look to determine whether music lessons have more of an effect on math subtests than on vocabulary subtests?
The interaction between music lessons and subtests (the music lessons X subtests interaction).
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