In Exercises 1.17-1.22, state whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case.

Aspirin and Cardiovascular Disease. In the article by P. Ridker et al. titled "A Randomized of Low-dose Aspirin in the Primary Prevention of Cardiovascular Disease in Women" (New England Journal of Medicine, Vol. 352, pp. 1293–1304), the researchers noted that "We randomly assigned 39,876 initially healthy women 45 years of age or older to receive 100 mg of aspirin or placebo on alternate days and then monitored them for 10 years for a first major cardiovascular event (i.e., nonfatal myocardial infarction, non-fatal stroke, death from cardiovascular causes)."

The given investigation is:

In the article by P. Ridker et al. titled "A Randomized of Low-dose Aspirin in the Primary Prevention of Cardiovascular Disease in Women" (New England Journal of Medicine, Vol. 352, pp. 1293–1304), the researchers noted that "We randomly assigned 39,876 initially healthy women 45 years of age or older to receive 100 mg of aspirin or placebo on alternate days and then monitored them for 10 years for a first major cardiovascular event.

The study in question is a Designed Experiment. The researchers used treatment and control groups on 39.876 women aged 45 and over, and followed them for a decade. The qualities were then observed and measurements collected.

We know that a designed experiment is applying treatments to experimental units, controlling extraneous sources of variation that could affect the experiment, and then observing features and taking measurements on the experimental units.

Therefore, the investigation in question is a Designed Experiment.