Problem-Solving and Data Analysis practice question

Answer: A. Researchers record which of 1,000 randomly selected adults drink coffee daily and compare the blood pressure of drinkers and non-drinkers.

In an observational study the researchers don't decide who does what; they record choices people have already made. Only choice A does that.

Why the other answers are wrong

B. Researchers randomly assign 1,000 adults either to drink coffee daily or to avoid it, then compare blood pressure.

Random assignment to drink or avoid coffee makes this an experiment.

C. Researchers give half of a group of volunteers a caffeine tablet and the other half a placebo, chosen by coin toss.

Assigning tablets by coin toss is an experiment.

D. Researchers assign each participant, by lottery, to one of three levels of daily coffee.

Assignment by lottery is an experiment.

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