PC Experimental Research A Threat to Internal Validity Discussion

A very important aspect of experimental research is the threat to internal validity. Read the following experiment along with its results and determine which threats, if any, might be operating in each of four experimental conditions. Remember, the threats to internal validity is mentioned in 7.5 of our chapter.

Dr. Wacko wanted to see whether sex, drugs, or rock and roll improved student self-esteem more than traditional counseling or no treatment at all over a six-week period. He randomly assigned four groups of 30 students to two groups. In all four groups the control group received no special treatment.

In Experimental Group A, he gave the students favorable information about illegal drug use, supplied them with quantities of several types of illegal drugs free of charge, and encouraged them to try the drugs.

In Experimental Group B, he told the students about the history of rock and roll and gave them MP3 players with a large quantity of rock and roll music. He also encouraged them to listen to the music at least six hours per day.

In Experimental Group C, he told the students the benefits of premarital sex and encouraged them to experiment with sexual behavior. He introduced them to attractive members of the opposite sex who had very liberal sexual attitudes. He also supplied them with contraceptives and private rooms. In Experimental Group D, he placed the students in traditional counseling to improve self-esteem.

Note: He measured self-esteem with a questionnaire in which self-esteem went from 0 = very negative to 100 = very positive. Here are his results; the number in parentheses () is the number of participants.

Self-Esteem Score and (Number of Students)

Pretest

Posttest

A Experimental

65 (15)

63 (13)

Control

60 (15)

66(14)

B. Experimental

65 (15))

89 (14

Control

45 (15)

79(14)

C. Experimental

66 (15)

90 (6)

Control

65 (15)

67(14)

D Experimental

64 (15)

88 (14)

Control

63 (15)

66 (15)