a study of treatments for angina (pain due to...

a study of treatments for angina (pain due to low blood supply to the heart) compared bypass surgery, angioplasty, and 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? we cant conclude that drugs prolong life because no placebo was used. we can conclude that drugs prolong life because the study was a comparative experiment. we cant conclude that drugs prolong life because the patients were volunteers. this study proves that drugs prolong life and should be the treatment of choice. we cant conclude that drugs prolong life because this was an observational study.

Answer

# Brief Explanations: This is an observational study as it only looks at existing medical - records of patients whose doctors had already chosen a treatment. There is no random assignment of treatments, so we cannot conclude causation. A placebo is not the main reason for not being able to conclude that drugs prolong life in this context. Volunteers or not is not the key issue here, and the study cannot prove drugs are the best treatment choice due to its observational nature. # Answer: We can't conclude that drugs prolong life because this was an observational study.