Guide to using the learning objectives
1.
Define1internal
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.
Explain2how
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.
Name1a
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."