Observational studies have suggested that vitamin E reduces risk of heart diseas
ID: 3220866 • Letter: O
Question
Observational studies have suggested that vitamin E reduces risk of heart disease. Careful experiments, however, showed that vitamin E has no effect. According to a commentary in the Journal of the American Medical Association: Thus, vitamin E enters the category of therapies that were promising in epidemiologic and observational studies but failed to deliver in adequately powered randomized controlled trials. As in other studies, the "healthy user" bias must be considered, ie, the healthy lifestyle behaviors that characterize individuals who care enough about their health to take various supplements are actually responsible for the better health, but this is minimized with the rigorous trial design. A friend who knows nothing about statistics asks you to explain this. a) What is the difference between observational studies and experiments? b) What is a "randomized controlled trial"? c) How does "healthy user bias" explain how people who take vitamin E supplements have better health in observational studies but not in controlled experiments?Explanation / Answer
a) In observational studies, we dont do any manipulation with the sample data. The data is studied as it is. In observational studies only correlation can be inferred. In experiments, the sample is usually divided into 2 separate groups - treated group and control group to observe the cause and effect relationship. In experimental settings causation can be inferred.
b) In ransomised control trial, participants are assigned to differnt groups only by chance without any influence. Participants are divided completely at random. Researcher as well as participants have no control over the assigment of the groups.
c) Healthy user bias is actually a sampling bias. The kind of people who enroll for these stuides are concerned of their health in general and are therefore not true representative of the population. So observational studies can detect false relationship between vitamin e supplements and heart disease. In control experiments sample is divided into 2 groups which can be done accounting for the healthy user bias. So equal no. of people can be assinged in both the control and treatment groups to account for this bias.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.