Statistics for the Behavioral Sciences by Frederick J. Gravetter, Larry B. Wallnau ISBN 10: 1305504917 ISBN 13: 9781305504912

SUMMARY 355
and the other group receiving treatment 2 followed by treatment 1. The goal of counterbalancing
is to distribute any outside effects evenly over the two treatments. For example,
if practice effects are a problem, then half of the participants will gain experience in treatment
1, which then helps their performance in treatment 2. However, the other half will
gain experience in treatment 2, which helps their performance in treatment 1. Thus, prior
experience helps the two treatments equally.
Finally, if there is reason to expect strong time-related effects or strong order effects,
your best strategy is not to use a repeated-measures design. Instead, use independentmeasures
(or a matched-subjects design) so that each individual participates in only one
treatment and is measured only one time.
LEARNING CHECK
1. An advantage of a repeated-measured design (compared to an independent-measures
design) is that it reduces the contribution of error variability due to ______.
a. M D
b. degrees of freedom
c. the effect of the treatment
d. individual differences
2. Compared to a repeated-measures design, which of the following is an advantage of
an independent-measures research design?
a. It usually requires fewer participants.
b. It eliminates the concern that performance in one treatment condition may be
influenced by experience in the other treatment condition.
c. It eliminates the concern that the participants in one treatment may be smarter
than those in the other treatment.
d. It tends to have a smaller variance and a smaller standard error.
3. For which of the following situations would a repeated-measures design have the
maximum advantage over an independent-measures design?
a. when many subjects are available and individual differences are small
b. when very few subjects are available and individual differences are small
c. when many subjects are available and individual differences are large
d. when very few subjects are available and individual differences are large
ANSWERS
1. D, 2. B, 3. D
SUMMARY
1. In a related-samples research study, the individuals
in one treatment condition are directly related,
one-to-one, with the individuals in the other treatment
condition(s). The most common related-samples study
is a repeated-measures design, in which the same
sample of individuals is tested in all of the treatment
conditions. This design literally repeats measurements
on the same subjects. An alternative is a matchedsubjects
design, in which the individuals in one sample
are matched one-to-one with individuals in another
sample. The matching is based on a variable relevant
to the study.