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

360 CHAPTER 11 | The t Test for Two Related Samples
PROBLEMS
1. For the each of the following studies determine
whether a repeated-measures t test is the appropriate
analysis. Explain your answers.
a. A researcher is examining the effect of violent
video games on behavior by comparing aggressive
behaviors for one group who just finished playing
a violent game with another group who played a
neutral game.
b. A researcher is examining the effect on humor on
memory by presenting a group of participants with
a series of humorous and not humorous sentences
and them recording how many of each type of
sentence is recalled by each participant.
c. A researcher is evaluating the effectiveness of
a new cholesterol medication by recording the
cholesterol level for each individual in a sample
before they start taking the medication and again
after 8 weeks with the medication.
2. What is the defining characteristic of a repeatedmeasures
or within-subjects research design?
3. Explain the difference between a matched-subjects
design and a repeated-measures design.
4. A researcher conducts an experiment comparing two
treatment conditions with 20 scores in each treatment
condition.
a. If an independent-measures design is used, how
many subjects are needed for the experiment?
b. If a repeated-measures design is used, how many
subjects are needed for the experiment?
c. If a matched-subjects design is used, how many
subjects are needed for the experiment?
5. A sample of n = 9 individuals participates in a
repeated-measures study that produces a sample mean
difference of M D
= 4.25 with SS = 128 for the difference
scores.
a. Calculate the standard deviation for the sample of
difference scores. Briefly explain what is measured
by the standard deviation.
b. Calculate the estimated standard error for the
sample mean difference. Briefly explain what is
measured by the estimated standard error.
6. In the Preview for Chapter 2, we presented a study
showing that a woman shown in a photograph was
judged as less attractive when the photograph showed
a visible tattoo compared to the same photograph with
the tattoo removed (Resenhoeft, Villa, & Wiseman,
2008). Suppose a similar experiment is conducted as
a repeated-measures study. A sample of n = 12 males
looks at a set of 30 photographs of women and rates
the attractiveness of each woman using a 5-point scale
(5 = most positive). One photograph appears twice
in the set, once with a tattoo and once with the tattoo
removed. For each participant, the researcher records
the difference between the two ratings of the same
photograph. On average, the photograph without the
tattoo is rated M D
= 1.2 points higher than the photograph
with the tattoo, with SS = 33 for the difference
scores. Does the presence of a visible tattoo have a
significant effect on the attractiveness ratings? Use a
two-tailed test with α = .05.
7. The following data are from a repeated-measures
study examining the effect of a treatment by measuring
a group of n = 6 participants before and after they
receive the treatment.
a. Calculate the difference scores and M D
.
b. Compute SS, sample variance, and estimated
standard error.
c. Is there a significant treatment effect? Use α = .05,
two tails.
Participant
Before
Treatment
After
Treatment
A 7 8
B 2 9
C 4 6
D 5 7
E 5 6
F 3 8
8. When you get a surprisingly low price on a product
do you assume that you got a really good deal or that
you bought a low-quality product? Research indicates
that you are more likely to associate low price and low
quality if someone else makes the purchase rather than
yourself (Yan and Sengupta, 2011). In a similar study,
n = 16 participants were asked to rate the quality of
low-priced items under two scenarios: purchased by
a friend or purchased yourself. The results produced
a mean difference of M D
= 2.6 and SS = 135, with
self-purchases rated higher.
a. Is the judged quality of objects significantly different
for self-purchases than for purchases made by
others? Use a two-tailed test with α = .05.
b. Compute Cohen’s d to measure the size of the
treatment effect.
9. Masculine-themed words (such as competitive,
independent, analyze, strong) are commonly used in
job recruitment materials, especially for job advertisements
in male-dominated areas (Gaucher, Friesen,
& Kay, 2010). The same study found that these