Guide to using the learning objectives


Learning Objectives for Chapter Nine – Internal Validity

 

Pages 254-266

 

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.

 

 

 

Pages 267-274

 

 

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.

 

Pages 274-276

 

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.”

 

 

 

 


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