1.      What feature of the matched-pairs design makes it

a.       an internally valid design?

Random assignment.

b.      a powerful design?


2.      A researcher uses a simple between-subjects experiment involving ten 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? How many degrees of freedom would the researcher have? What type of matching task would you suggest? 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).

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).

3.      An investigator wants to find out whether hearing jokes will allow a person to persevere longer on a frustrating task.  The researcher matches participants based on their reaction to a frustrating task. Of the thirty original participants, five quit the study after going through the "frustration pretest"  Beyond the ethical problems, what problems are there in using a matched pairs design in this situation?

The drop-out rate poses problems for generalizing the results. In addition, the frustration pretest may have sensitized participants to what the study was about.

4.      What problems would there be in using a within-subjects design to study the "humor-perseverance" study (discussed in question 3)? Would a counterbalanced design solve these problems?

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). 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.

5.      Why are within-subjects designs more powerful than matched-pairs designs?

Because they do a better job of reducing the effects of between subject differences (by eliminating them) and because they get more observations per participant.

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.

7.      A student hypothesizes that alcohol level will affect sense of humor.  Specifically, the student has two hypotheses.  First, the more people drink, the more they laugh at slapstick humor.  Second, the more people drink, the less they will laugh at other forms of humor. What design would you recommend the student use? Why?

Completely between-subjects design because sensitization is a big problem (participants can figure out the hypothesis and play along). In addition, order effects may occur (participants may have their fill of slapstick). We do not recommend counterbalancing because counterbalancing the alcohol variable would be difficult.

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.

9.      Using a driving simulator and a within-subjects design, you want to compare the differences between driving unimpaired, driving while talking on a cell phone, and driving while legally intoxicated.

a.       Which order effects do you have to worry about? Why?

Practice (as participants get used to the simulator), fatigue (as participants get bored with the task), and carryover (from the drinking trial to later trials).

b.      To what degree would counterbalancing solve the problems caused by order effects?

Counterbalancing might be able to control for practice and fatigue. However, counterbalancing could not balance out the carryover effects from drinking.

c.       How would you try to prevent order effects from harming the validity of your study?

Giving participants practice on the task to minimize practice effects, making the simulation short to minimize fatigue, and putting the trials two days apart to minimize carryover effects.

10.  A researcher wants to kow 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.