Guide to using the learning objectives
1.
Define1
internal validity. Explain2 how extraneous factors can harm internal validity.
2.
Explain2
why selection is a serious threat to designs that compare a treatment group to
a no-treatment group. Then, explain why the following do not eliminate
selection as a threat to such designs.
a. Self-assignment to group
b. Researcher assignment to group
c.
Arbitrary
assignment to group
d. Matching participants on all
variables
e. Matching participants on all
relevant variables
f.
Matching
participants on pretest scores (in addressing the problems of matching
participants on pretest scores, be sure to discuss selection by maturation
interactions and regression).
3.
Explain2
how mortality can ruin the internal validity of a treatment group versus
no-treatment group study.
4.
At a
picnic, some children are given high-sugar snacks, whereas others are given
low–sugar snacks. Of the children who complete the study, those in the
“high sugar” condition are judged to be more irritable than the
group in the “low sugar” group. One explanation for the results is
that sugar caused the difference between the groups. Using what you know about
the problems with two-group studies, generate5 alternative
explanations for the results of this study.
5.
Suppose
that a study finds that individuals who have purchased home gym equipment in
the last three months are more fit than those who have not. One explanation for
the difference between groups is that the exercise equipment has caused the difference
between the groups. Using what you know about the problems with two-group
studies, generate5 alternative explanations for the results of this
study.
6.
Describe2
four factors that could cause participants to change between pretest and
posttest.
7.
Describe2
three reasons that participants’ scores might change from pretest to
posttest even though the treatment had no effect.
8.
Distinguish4
between history and maturation.
9.
Distinguish4
between testing and instrumentation.
10.
At a
picnic, some children are given high-sugar snacks. An hour later, those
children are judged to be more irritable than they were before they were given
the sugar. One explanation for the results is that sugar caused the change in
the children’s behavior. Using what you know about the problems with
pretest-posttest studies, generate5 alternative explanations for the
results of this study.
11.
Suppose
that a study finds that individuals who have purchased home gym equipment in
the last three months are more fit (as measured by their performance on the
machine they purchased) than they were before they purchased the equipment. One
explanation for the change is that the exercise equipment has made them more
fit. Using what you know about the problems with pretest-posttest designs,
generate5 alternative explanations for the results of this study.
12.
Explain2
why extraneous variables cannot be eliminated from a study.
13.
List1
the eight categories into which all extraneous variables fall.
14.
Name1
a method that, when used with statistics, allows one to rule out the effects of
extraneous variables.
15.
Defend4
the following statement: “Researchers should focus on internal validity
rather than on external validity.”