State whether the investigation in question is an observational study or a designed experiment. Justify your answer. In a paper in a medical journal, researchers 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 1300 patients were randomly assigned in a 1:2:1 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