1.
Steinberg and Dornbusch
(1991) find that there is a positive correlation between cutting class and
hours of week adolescents work. In addition, they find
a negative correlation between grade point average and number of hours worked.
a.
Describe, in your own words, what
the relationship is between class-cutting and hours of week adolescents
work.
Hint #1: The more students work, the _____ likely they are to cut class.
Hint #2: You can easily answer this question by using this tool.
b.
Describe, in your own words, what
the relationship is between grade point average and hours of week adolescents work.
Hint #1: The more students work, the _____ their grade point average.
Hint #2: You can easily answer this question by using this tool.
c.
What conclusions can you draw
about the effects of work? Why?
d.
If you had been analyzing their
data, what analysis would you use? Why?
To know what analysis to use, look at Box 7.3 on page 257 (focus on the far right column). To understand why you should do that analysis, see "The Case Against Doing a Median Split" on the bottom of p. 252.
2. Steinberg & Dornbusch (1991) also reported that the correlation between hours of employment and interest in school was statistically significant. Specifically, they reported that r(3,989)= -.06, p <.001. [Note that the r (3,989) means that they had 3,989 participants in their study.] Interpret this finding.
The more hours students worked, the less likely they were to be interested in school. However, this effect was extremely small and is only significant because the researchers, by using almost 4,000 participants had an extremely powerful design. The effect is so small that for practical purposes it is meaningless. Put another way, the coefficient of determination is only .0036, meaning that the relationship explains almost none (0.0036 is not that far from 0.00) of the variation in interest in school.
3.
Brown (1991) found that a measure
of aerobic fitness correlated +.28 with a self-report measure of how much
people exercised. He also found that the measure of
aerobic fitness correlated -.41 with resting heart rate. Is
resting heart rate or self-report of exercise more closely related to the
aerobic fitness measure?
Hint #1: You may need all four hints to answer this question.
Hint #2: To determine the strength of a relationship, do you care whether the sign is positive or negative? (If you are not sure how to answer this question, see Summary point #14 on page 272).
Hint #3: To determine a difference between two things, can you just eyeball the data--or do you need to do a statistical significance test to determine whether the difference is reliable?
Hint #4: An acceptable answer might include saying that one would need to do a statistical analysis to determine whether there was a statistically significant difference between the two correlations.
4. In the same study, sex was coded as 1= male, 2= female. The correlation between sex and aerobic fitness was
-.58,
which was statistically significant at the p<.01 level.
a.
In this study, were men or women
more fit?
Men were more aerobically fit.
b.
What would the correlation have
been if sex had been coded as 1= female and 2= male?
+.58.
c.
From the information we have
given you, can you conclude that one gender tends to be more aerobically fit
than the other? Why or why not?
No, because you do not know if the sample of men and
women were a representative random sample of all men and women.
5. This is an open-ended question, so you have a lot of freedom in how to answer it. You should, however, try to get
a representative sample of ads (preferably by having a large, random sample) and
an objective coding scheme (see p. 236).
6.
A physician looked at 26
instances of crib death in a certain town. The
physician found that some of these deaths were due to parents suffocating their
children. As a result, the physician concluded that
most crib deaths in this country are not due to problems in brain development,
but to parental abuse and neglect. What problems do
you have with the physician's conclusions?
First, the physician generalized from a small and
limited sample to the entire country. Second, the
physician made an inference about the percentage of instances in a larger
population (that most crib deaths are due to parental neglect) without doing
any statistical test of this assertion.
7.
Researchers began by looking
at how a sample of 5-year-olds were treated by their parents.
Thirty-six years later, when the participants were 41-year-olds, the
study examined the degree to which these individuals were socially accomplished. The investigators then looked at the relationship between
childrearing practices when the child was 5 and how socially accomplished the
person was at 41 (Franz, McClelland, & Weinberger, 1991).
They concluded that having a warm and affectionate father or mother was
significantly associated with “adult social accomplishment.”
a. What advantages does this prospective study
have over a study that asks 41-year-olds to reflect back on their childhood?
Hint: See the first four bullet points under point #3 of Box 7.2 on p. 229.
b. How would you measure adult social accomplishment?
Hint: Define adult social social accomplishment and then come up with objective and self-report measures that fit your definition.
c. How would you measure parental warmth? Why?
Hint: Define parental warmth and then come up with objective and self-report measures that fit your definition.
d. Assume, for the moment, that the study clearly established a relationship between parenting practices and adult social accomplishment. Could we then conclude that parenting practices account for (cause) adult social accomplishment? Why or why not?
Hint: See summary point 2 on page 272.
e. Imagine that the researchers had failed to
find a significant relationship between the variables of adult social
accomplishment and parental warmth. What might have
caused their results to fail to reach significance?
A nonsignificant result could occur for at least four reasons. Those four reasons are listed in summary point #19 on page 273 and explained on pages 266-267.
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