QuestionSBA
QuestionChoice
This is incorrect as this is the risk of developing diabetes in the placebo group
32551
d
0.72
QuestionChoice
The relative risk or risk ratio is the probability of an outcome occurring in a patient group exposed to a change (in this case, a new drug). Of those given the drug, 50% went on to develop diabetes compared to 72% in the placebo group.

Relative risk = risk in the group exposed to drug/risk in those not exposed to the drug.

50/72 = 0.69
32548
a
0.69
QuestionChoice
This is incorrect as this is the risk of not developing diabetes in the placebo group
32552
e
0.28
QuestionChoice
This is incorrect as this is the risk of developing diabetes in the group given the drug
32550
c
0.50
QuestionChoice
This is incorrect as the group that has been exposed to the change is those given the drug
32549
b
1.44
Concept
Chapter
# Definition

Risk in medical statistics refers to the probability of an outcome (either good or bad) occurring within a studied population. There are several different types of risk that are often used in medical studies.

# What is Risk/Prevalence?

This is simply the probability of an event occurring within a defined population.

# What is Risk Ratio (RR)?

The risk ratio (also known as relative risk) is the probability of an event occurring in an exposed group compared to the probability occurring in a non-exposed group.

The risk ratio is calculated by finding the ratio of incidence of a disease amongst the exposed population and the incidence amongst the non-exposed population.

Risk ratios are used in cohort studies and in interventional studies in which the experimenter intervenes at some point during the study, such as in randomised controlled trials and pre-post studies.

However, in cross-sectional studies and case-control studies, the incidence of the disease in the exposed and unexposed populations cannot be found, since the data only provides the cases and controls.

Consequently,the risk ratio cannot be calculated for case-control studies and cross-sectional studies. Instead, an odds ratio must be found.

# What is Absolute Risk Reduction (ARR)?

The absolute risk reduction is the absolute difference in the risk between the control group and the experimental group. It tells you in absolute terms how much an intervention changes an outcome of interest.

# Calculation of Absolute Risk Reduction

It is calculated as follows:

_ARR = Risk(control group) - Risk(experimental group)_

A given ARR is generally considered significant if the 95% confidence interval does not cross 0.

ARR can then be used to calculate the number needed to treat (NNT).

# What is Relative Risk Reduction (RRR)?

The relative risk reduction can be thought of as the proportional reduction in risk bestowed by the intervention compared to the control situation. It is more useful in helping you understand the efficacy of an intervention when the absolute risk of outcomes are rare (for example when considering the benefits of a statin for reducing MI in a given population).

# Calculating RRR

It is calculated as follows:

_RRR = 1 - [Risk(Experimental group) / Risk(Control group)]_

A given RRR is generally considered significant if the 95% confidence interval does not cross 1.
594
608
Risk
Topic
51
Medical Statistics
6510
Relative risk compares the likelihood of an event occurring in an exposed group to an unexposed group, calculated as the ratio of incidence in the exposed group to the unexposed group.
A new drug is developed that claims to prevent diabetes mellitus in patients with impaired glucose tolerance. A randomised control trial is undertaken in 100 patients with HbA1c of 42-47, where half the participants are given the new drug, and the other half are given a placebo.

In those who were given the new drug, 25 patients developed diabetes within five years; in the group who were not given the drug, 36 patients developed diabetes within five years.

What is the relative risk of developing diabetes if treated with the new drug?
a