Deck 11: Randomized Trials: Some Further Issues

Question 1

Epidemiologists decided to investigate the effect of sunscreens on sunburns.They ran an epidemiologic study to see the association of sunscreens and sunburns.Overall,460 people have enrolled in the study.Investigators randomly allocated 230 people to the treatment group (sunscreens) and 230 to the control group (placebo).They exposed those 460 people to the high mountain trail on a sunny day.At the end of the study,30 people developed sunburns in the sunscreen group and 130 people developed sunburns in the placebo group.What type of study design is this?

A) Cross-sectional study
B) Prospective cohort study
C) Case-control study
D) Randomized trial
E) Case-control study

Answer 1

D
Investigators randomly allocated the exposure status to the participants.Therefore it is a randomized trial."Cross-sectional study" is not correct because they did not capture exposure and outcome status at the same time."Prospective cohort study" is not correct because they did not recruit the people based on their exposure status."Case-control study" is not correct because they did not define the people based on their outcome status."Case-control study" is not correct because they did not report a case or series of cases.

Question 2

What is the primary purpose of randomization?

A) To prevent bias in the assignment of treatment
B) To provide a probability basis for statistical testing
C) To ensure the same number of people are randomized to each group
D) To ensure that the subjects not to know which group they are assigned to
E) To guarantee the comparability of the different treatment groups

Answer 2

A
The primary purpose of randomization is to reduce the bias from investigator to assign the treatment to participants."To provide a probability basis for statistical testing" is not correct.Probability basics are not related with randomization."To ensure the same number of people are randomized to each group" is not correct.The same number of people to each group can be guaranteed by other ways such as exclusion or dropping participants."To ensure that the subjects not to know which group they are assigned to" is not correct and this is a description of blinding (masking)."To guarantee the comparability of the different treatment groups" is not correct.Even though randomization increases the comparability of different treatment group,it cannot guarantee the comparability and it is not the primary purpose of randomization.