Question

in a RCT study, incidence of disease in new treatment was 2/100/year, in control group incidence of disease was 3/100/year. which is correct:

a) new treatment protects against disease better since RR<1

b) control group had 50% higher risk for disease compared to new treatment group

c) both a and b are correct

d) both a and b are incorrect

Answer 1

RR is the relative risk. It is defined by the ratio of probability of incidence of disease when subjected to new treatment to the probability of incidence of disease when in a control group.

So RR is given by

Since the relative risk is less than 1 , it means that the new treatment protects against the disease in a better way.

Hence, option a is correct.

Risk for disease when subjected to new treatment = 2/100 = 0.02

Risk for disease when in control group = 3/100 = 0.03

Difference in risk = 0.03-0.02 = 0.01

Percentage difference in risk of the control group compared to the new treatment

Hence, the control group has 50% higher risk of disease as compared to the new treatment.

Hence, option b is also right.

So the correct option is option c , that is, both options are correct.

Thank you.

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