QuestionSBA
QuestionChoice
Relative risk reduction shows how much the treatment has reduced the risk of bad outcomes relative to the control. The risk reduction is (20-12%)/20% = 0.4 or 40%, i.e. a patient is 40% less likely to develop a colitic flair within the next year by taking the drug vs taking a placebo
33048
a
40%
QuestionChoice
If the treatment causes an increased risk of bad outcome, then it is termed the "relative risk increase". 66.7% would be the relative risk increase if the treatment arm resulted in 20% of colitic flares within 1 year and the placebo arm resulted in 12%
33050
c
66.7%
QuestionChoice
8% corresponds to the absolute relative risk, calculated as 20%-12%. This means that if you treated 100 people with this drug, 8 would be prevented from having a colitic flare in the next year. The number needed to treat (NNT) is calculated from this figure as 100/8 = 12.5, i.e. 12.5 people would need to be treated with this drug to prevent one episode
33049
b
8%
QuestionChoice
60% is the value of the relative risk (in percentage form). Relative risk is a proportional measure to determine the size of effect of a treatment compared to other interventions or a control. It is the proportion of bad outcomes in the intervention group divided by the proportion of bad outcomes in the control group. In this case 12%/20% = 0.6
33051
d
60%
QuestionChoice
140% relative risk reduction cannot exist as the maximum reduction of any bad outcome is 100%
33052
e
140%
QuestionComment
Do you usually measure relative risk or relative risk reduction in RCTs? 
59004
QuestionComment
relative risk usually but can use relative risk reduction for interpretation in papers etc
60381
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# 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.
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Risk
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Medical Statistics
6610
Relative risk reduction (RRR) is a measure of how much the risk of an event is reduced in the treatment group compared to the control group, calculated as 1 minus the relative risk (RR) and expressed as a percentage: RRR = (1 - RR) × 100, where RR is the risk in the treatment group divided by the risk in the control group.
A new treatment has been developed for ulcerative colitis. In a large randomised controlled trial, 20% of participants in the placebo arm had an acute flare within the next year. In the treatment arm, 12% of participants developed an acute flare within the next year.

What is the relative risk reduction of the new treatment?
a