Question

ch 9 in order to investigate treatments for morbid obesity, obese subjects satisfying fairly strict requirements were randomly assigned to one of three groups: (1) gastric bypass surgery, (2) participation in a diet and exercise program, or (3) both gastric bypass surgery and participation in the diet and exercise program. researchers carefully observed the amount of weight lost five years after the study began. this study uses the principles of

• blocking.
• randomization.
• replication
• confounding.

Explanation:

1. Analyze each option:

• Blocking: Involves grouping similar subjects first, then randomizing within blocks. The study here directly randomizes subjects to groups without prior blocking, so not blocking.
• Randomization: The study randomly assigns subjects to three groups (gastric bypass, diet/exercise, or both). This matches the principle of randomization (assigning experimental units randomly to treatment groups to reduce bias).
• Replication: Involves repeating the experiment or having multiple subjects in each group to increase reliability. The question focuses on assignment, not replication.
• Confounding: Occurs when an extraneous variable affects the response, making it hard to tell treatment effects. The study's design is about random assignment, not confounding.

1. Conclusion: The key action here is random assignment of subjects to groups, so the principle is randomization.

Answer:

B. randomization