A threat to internal validity of a study using a two-group ...

[DelorasTo]

A threat to internal validity of a study using a two-group pretest-posttest design is that:
 
  a. external events are extremely likely to affect the outcome of these studies.
  b. people are more likely to drop out of this type of study.
  c. the pretest may sensitize subjects so they change their behavior or responses on the posttest.
  d. there is no way to determine if the groups are alike before starting the study.

Question 2

At the beginning and end of a 10-week exercise program the subjects have their lung vital capacity measured by the researchers. The readings are plotted on a graph and then the results are recorded.
 
  Which of the following can pose a threat to the internal validity in this study?
  a. Instrumentation
  b. Selection
  c. Setting
  d. Testing

[potomatos]

Answer to Question 1

ANS: C
Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables. In this example, the fact that subjects have taken the pretest may affect their response to the posttest.
External events are not a threat to the internal validity of this design. Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables.
Dropout would depend on the time between the pretest and posttest. Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables.
The determination of whether or not two groups are more similar than different is oftentimes the focus of the study. Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables.

Answer to Question 2

ANS: A
Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables. In this example the researchers must be concerned about the reliability of the instrument measuring the subjects' lung vital capacity.
Subjects are acting as their own controls. Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables. In this example the researchers must be concerned about the reliability of the instrument measuring the subjects' lung vital capacity.
Setting would be the same in this description. Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables. In this example the researchers must be concerned about the reliability of the instrument measuring the subjects' lung vital capacity.
Testing occurs with prescribed time periods in between. Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of the effects of extraneous variables. In this example the researchers must be concerned about the reliability of the instrument measuring the subjects' lung vital capacity.