Question

in a study of 135 women, roughly half took estrogen as well as calcium and vitamin d supplements and received regular checkups. the remaining women received the supplements and the checkups but substituted a sugar pill for the estrogen. those who received the estrogen had an average 3.6 percent gain in bone density compared to a 0.2 percent bone density improvement in those taking the sugar pill. this study can best be described as
a controlled placebo experiment
a survey using simple random sampling
the placebo effect
a census
a survey using quota sampling
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Explanation:

A controlled placebo experiment has two groups. One group gets the treatment (here, estrogen) and the other gets a placebo (sugar pill). Both groups have other factors (supplements and check - ups) controlled. A survey involves asking questions. The placebo effect is when a person improves because they think they are getting treatment. A census is a study of an entire population. Quota sampling is a non - random sampling method. In this study, there are two groups (one with estrogen - treatment, one with sugar pill - placebo) with other variables (supplements and check - ups) kept the same.

Answer:

a controlled placebo experiment