A tamoxifen study claims that a combination of chemotherapy and the hormone therapy tamoxifen is more effective than tamoxifen alone in preventing breast cancer. In the study, a group of researchers from the U.S. and Canada studied 1477 postmenopausal women with early-stage breast cancer. The women were randomly assigned to one of three study groups. Group A (361 patients) received tamoxifen alone on a daily basis for five years. Group B (566 patients) received chemotherapy and tamoxifen for six months, and then completed five years of tamoxifen treatment. Group C (550 patients) received chemotherapy alone for six months followed by five years of tamoxifen treatment. All 1477 patients knew which treatment they were receiving.This study can best be described as a

Question

A. survey using stratified sampling.
B. randomized controlled experiment.
C. census.
D. survey using quota sampling.
E. survey using simple random sampling.

Answer 1

Answer: B