A number of studies have been conducted over the years to determine whether vita

Question

A number of studies have been conducted over the years to determine whether vitamins or other micronutrients can decrease the risk of cancer, heart disease, and stroke. The results have not been encouraging. Klein and colleagues (2013) report the results of a randomized clinical trial (RCT) called the Selenium and Vitamin E Cancer Prevention Trial (SELECT). Men from 427 study sites were randomized between August 22, 2001, and June 24, 2004, to one of four groups:

1. vitamin E only (n=8,737); 2. selenium only (n=8,752); 3. both vitamin E and selenium (n=8,702); or 4. placebo (n=8,696).

To be eligible, subjects had to have a negative PSA test (<4.0 ng/ ml), a negative digital rectal exam, and be either 50 years and older (blacks), or 55 years and older (all other races).

Questions

1. What is a randomized clinical trial? Why would we want to randomize?

2. What is the control group in this RCT? What other kinds of control groups exist in RCTs?

3. The study used a randomized block design in which a “block” was one of the 427 study sites. Such a design ensures a balance of the four groups in each study site. Each site supplied an average of 83 men. Suppose Study Site A recruited 100 men—how many men would be receiving both vitamin E and selenium?

4. Stratified randomization is similar, although it may involve more than one variable. Suppose the study was block randomized but also stratified by age (<65 and >65) and that you wanted 60 percent of men to be under 65. Of the 100 men in Study Site A, how many men under 65 would be in the placebo group?

Randomization precludes subjects choosing which treatment arm they would want to join. Subjects would choose one treatment arm versus another for numerous reasons, and because many of those reasons could have an impact on outcomes, this is a form of selection bias.

Questions

5. Suppose that this were a cohort study and not an RCT, and that subjects were allowed to self-select into the four groups. Further assume that the more health-conscious subjects (i.e., those with a lower body mass index [BMI] and better dietary habits) would have a higher probability of choosing the vitamin E and/ or selenium groups, and that lower BMI and better dietary habits decrease the risk of prostate cancer. What would be the effect? of this bias on the outcomes of the study (i.e., the treatment effect)?

6. The prostate cancer screening test (PSA) and digital rectal exam (DRE) were required at entry to the study but only encouraged annually during follow-up. Again, suppose that subjects were allowed to self-select into groups, that the vitamin E groups had a higher probability of having annual DRE and PSA tests, and that these tests detected cancer earlier and at a more indolent stage. How would this affect the study results?

7. Some randomized trials intentionally switch subjects from treatment to control group and vice-versa at some point, although the SELECT study did not do this. What are these trials called? Identify some of the limitations of these kinds of trials.

8. The main outcome measure, or primary endpoint, in the SELECT study was the incidence of prostate cancer. Other secondary outcomes included lung, colorectal, and overall primary cancer; all-cause mortality; diabetes; and cardiovascular event. How would we measure a primary treatment effect and secondary treatment effects from these outcomes?

Explanation / Answer

RANDOMIZES CLINICAL TRIAL :

it is also called as randomised controlled trail , which is a scientific experiment which aims to reduce bias when testing a new treatement. People participating are in trail are randomly allocated to either, group recieving treatement under investigation or to the group receiving standard treatement under control.

RANDOMIZATION minimises the selection bias and different comparison group allows the researchers to determine effect of treatement when compared with no treatemnt (control) group , while other variables are kept constant .

2. CONTROL GROUP IN RCT

control group is a group in a study or experiment that doesn't receive treatment by researchers and then they are used as benchmark to measure how other subhjecys do . They are left untreated or unexposed to procedures .This is done to know about the effectiveness of the drug

TYPES OF CONTROL GROUP

A)placebo B)no tratement C) different dose or regimen of study treatemnt    D) a different active treatement

3. suppose there are x people then according to the data given :

x*4 / 427= 100

therefore . x= 11,000 (approx)

4.

rest can be done similarly ,if any queries , feel free to ask

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