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.

Heart Failure. In the paper "Cardiac-Resynchronization Therapy with or without an Implantable Defibrillator in Advanced Chronic Heart Failure" (New England Journal of Medicine, Vol. 350, pp. 2140-2150), M. Bristow et al. reported the results of a study of methods for treating patients who had advanced heart failure due to ischemic or nonischemic cardiomyopathies. A total of 1520 patients were randomly assigned in a 1:2:2 ratio to receive optimal pharmacologic therapy alone or in combination with either a pacemaker or a pacemaker-defibrillator combination. The patients were then observed until they died or were hospitalized for any cause.

The given investigation is:

In the paper "Cardiac-Resynchronization Therapy with or without an Implantable Defibrillator in Advanced Chronic Heart Failure", M. Bristow et al. reported the results of a study of methods for treating patients who had advanced heart failure due to ischemic or nonischemic cardiomyopathies. A total of 1520 patients were randomly assigned in a 1:2:2 ratio to receive optimal pharmacologic therapy alone or in combination with either a pacemaker or a pacemaker-defibrillator combination.

The patients were then observed until they died or were hospitalized for any cause.

From the given investigation:

A total of 1520 patients were randomly selected to undergo optimal pharmacologic therapy alone or in combination with a pacemaker or pacemaker-defibrillator mix in a 1.2:2 ratio. The patients were then kept under observation until they died or were admitted to the hospital for whatever reason.

This is a designed experiment, in which researchers impose treatments and controls, then observe and quantify characteristics. Experiments aiming to establish causation can be beneficial.