A researcher believes that therapy is more effective if patients ...

[silviawilliams41]

A researcher believes that therapy is more effective if patients exercise.
 
  He tells his patients that he has arranged for them to use the hospital gym, if they so desireand that if they are interested, they will then be in the experimental group. This represents which threat to internal validity?
  a. Maturation
  b. Reliability of the implementation
  c. History
  d. Selection

Question 2

A researcher uses matching to constitute his control group, while performing a study on psychotherapy as an adjunct treatment for substance addiction. What type of validity might be enhanced by matching, in this instance?
 
  a. Construct validity
  b. Statistical conclusion validity
  c. External validity
  d. Internal validity

[lgoldst9]

Answer to Question 1

ANS: D
Selection addresses the process by which subjects are chosen to take part in a study and how subjects are grouped within a study. A selection threat is more likely to occur in studies in which random assignment is not possible. In some studies, people selected for the study may differ in some important way from people not selected for the study. In other studies, the threat is due to differences in subjects selected for study groups. In this study, subjects choose to be in the experimental group because they were willing to exercise; in this way, they differ from the rest of the grouppossibly they are less depressedand this could introduce bias into the study.

Answer to Question 2

ANS: D
Matching is used when a subject in the experimental group is randomly selected and then a subject similar in relation to important extraneous variables is randomly selected for the control group. For example, subjects in the experimental and control groups might be matched for age, gender, severity of illness, or number of chronic illnesses. Statistical conclusion validity is concerned with whether the conclusions about relationships or differences drawn from statistical analysis are an accurate reflection of the real world: it is not affected by use of matching. Internal validity is the extent to which the effects detected in the study are a true reflection of reality rather than the result of extraneous variables: matching can increase internal validity if the researcher can correctly identify the principal extraneous variables. Construct validity examines the fit between the conceptual definitions and operational definitions of variables: matching has no effect on this. External validity is concerned with the extent to which study findings can be generalized beyond the sample used in the study; matching does not affect external validity, to any extent.

[silviawilliams41]

Excellent

[steff9894]

Gracias!