Question

does regularly taking aspirin help protect people against heart attacks? does regularly taking beta - carotene help prevent cancer? the physicians health study i was a medical experiment that helped answer these questions. the subjects in this experiment were 21,996 male physicians. each of the physicians was assigned to take an aspirin or an aspirin - like placebo. likewise, each of the physicians was assigned to take beta - carotene or a beta - carotene - like placebo. the physicians were followed for several years and researchers recorded if each of the physicians had a heart attack or developed cancer.

1. why was it necessary to perform an experiment rather than simply asking the doctors whether or not they take aspirin and beta - carotene regularly?
2. identify the four treatments in this experiment.
3. explain the purpose of the control group in this experiment.

Explanation:

1. Asking doctors may lead to recall bias (they might misremember) and confounding variables (other lifestyle factors they don't mention). An experiment controls variables better.
2. The four treatments are: aspirin + beta - carotene, aspirin + beta - carotene - like placebo, aspirin - like placebo + beta - carotene, aspirin - like placebo + beta - carotene - like placebo.
3. The control group (those taking placebos) is used for comparison. It helps determine if the effects (e.g., fewer heart attacks or less cancer) are due to the actual treatments (aspirin or beta - carotene) and not other factors.

Answer:

1. To control variables and avoid biases.
2. Aspirin + beta - carotene; Aspirin + beta - carotene - like placebo; Aspirin - like placebo + beta - carotene; Aspirin - like placebo + beta - carotene - like placebo.
3. To provide a comparison baseline.