The Basic Experiment

In an effort to help prevent childhood obesity, some researchers have developed behavioral interventions. In one school program, nutrition researchers wanted to teach children to make healthier food choices in the cafeteria. They developed a short training program that involved a 20-minute interactive video. To test the effectiveness of this video training program, the researchers designed a study with an experimental condition, in which school children in first grade were exposed to the new program, and a control condition, in which children watched a 20-minute cartoon having nothing to do with nutrition.A food choice test measured the children's behavior in their real school cafeteria. Each food line presented

four choice points, in which a healthier option (e.g., fruit) competed against a less healthy option (e.g., vanilla pudding). By closely observing a child as he moved through the cafeteria line, a researcher (a graduate student) marked down the number of healthy options a child selected. A child could get a score from zero (child made no healthy choices) to four (child made the healthy choice at all choice points).

Below are four descriptions of variations on the study described above.

a. Identify the design as pretest-posttest, posttest only, or repeated measures. (Just indicate A, B, or C.)

b. Identify the threats to internal validity in each design. Possible threats include history, maturation, testing, instrumentation, attrition, regression to the mean, selection, experimenter expectancy. (Again, indicate A, B, C, or D.)

c. Draw a sketch of each design, using the tic-tac-toe notation discussed Lecture.

Variation 3:

During a class early in the school year, all the children viewed the 20-minute cartoon (control condition). Two days later, the food choice test was conducted. The experimenter fell ill soon afterward, and so it wasn't until a class late in the school year that all the children viewed the 20-minute interactive video (experimental condition). Two days after that, a second food choice test was conducted. The mean score for the children on the first food choice test was 1.0and their mean score on the second food choice test was 3.5. We conclude that the 20-minute interactive video improved children's food choices.

7.The design is ________________.

A)pretest-posttest

B)posttest only

C)repeated measures

8.The largest threat to internal validity for this design is _________________.

A) attrition

B)testing

C)instrumentation

D) History

9.Sketch the design using tic-tac-toe notation. (Be sure to define the notation you use.)