A study of treatments for angina (pain due to low blood supply to the heart) compared bypass surgery, angioplasty, and the use of drugs. The study looked at the medical records of thousands of angina patients whose doctors had chosen one of these treatments. It found that the average survival time of patients given drugs was the highest. What do you conclude?

(a) This study proves that drugs prolong life and should be the treatment of choice.

(b) We can conclude that drugs prolong life because the study was a comparative experiment.

(c) We can’t conclude that drugs prolong life because the patients were volunteers.

(d) We can’t conclude that drugs prolong life because this was an observational study.

(e) We can’t conclude that drugs prolong life because no placebo was used.

By examining the medical records of patients who were treated for one of the treatments, a study for angina was done that compared bypass surgery to the usage of medications.

The random assignment method assigns subjects to treatments based on chance. Before the treatments are applied, random assignment establishes treatment groups that are comparable (except for chance variance). In experiments, randomization and comparison combined prevent bias or systematic favoritism.

By examining the medical records of patients who were treated for one of the treatments, a study for angina was done that compared bypass surgery to the usage of medications. It was determined that patients who were treated with medications had the best chance of surviving.

The researchers are not attempting to influence the outcome by allocating participants to treatment or control groups at random, but rather by observing the treatments. As a result, the research is observational. There are a lot of potential confounders here. As a result, it is impossible to establish that medications help people live longer. As a result, the best solution is (d).