What is meant by relative risk reduction in epidemiology?
Relative risk reduction. In epidemiology, the relative risk reduction (RRR) or efficacy is the relative decrease in the risk of an adverse event in the exposed group compared to an unexposed group. It is computed as , where is the incidence in the exposed group, and is the incidence in the unexposed group.
What is the relative risk reduction (RRR) of exposure?
The group exposed to treatment (left) has the risk of an adverse outcome (black) reduced by 50% (RRR = 0.5) compared to the unexposed group (right). In epidemiology, the relative risk reduction (RRR) or efficacy is the relative decrease in the risk of an adverse event in the exposed group compared to an unexposed group. It is computed as
What is the reciprocal of 1/absolute risk reduction?
The reciprocal of this value (1/absolute risk reduction) gives the number of patients who need to be treated for a certain period of time to prevent one event. This is termed the number needed to treat and can be useful for comparing the effectiveness of a number of different interventions.
How do you calculate relative risk reduction?
The relative risk reduction equals the amount by which the relative risk has been reduced by treatment and is calculated as 1 – relative risk. For example in the sheepskin trial, sheepskin overlays reduced the risk of patients getting ulcers by 0.42 (1 – 0.58) or 42%.
What does a relative risk of 0.25 mean?
Similarly a risk ratio of 0.25 is interpreted as the probability of an event with treatment being one-quarter of that without treatment. This may be expressed alternatively by saying that treatment decreases the risk of events by 100 × (1 –RR)% = 75%.
Is relative risk the same as relative risk reduction?
Sometimes the outcome is a good one and the interpretation of relative risk is the opposite of what we have just outlined. Relative risk reduction (RRR) tells you by how much the treatment reduced the risk of bad outcomes relative to the control group who did not have the treatment.
What does a relative risk of 0.3 mean?
An RR that is less than 1.00 means that the risk is lower in the exposed sample. An RR that is greater than 1.00 means that the risk is increased in the exposed sample. 3. An RR of, say, 0.3 can be expressed in plain English in many ways.
How do you calculate relative risk reduction and absolute risk reduction?
How to calculate riskAR (absolute risk) = the number of events (good or bad) in treated or control groups, divided by the number of people in that group.ARC = the AR of events in the control group.ART = the AR of events in the treatment group.ARR (absolute risk reduction) = ARC – ART.RR (relative risk) = ART / ARC.More items...
How do you calculate risk reduction?
Relative Risk Reduction = |EER-CER|/CER For example, say the disease A occurs in 1 in 100,000 people but taking drug X reduces the incidence to 1 in 10,000,000. The absolute risk of disease is 0.001%. The relative risk is 0.00001/0.001 = 0.1 and the relative risk reduction is 1- 0.1 = .
What does a relative risk of 1.5 mean?
What relative risk tells us. A relative risk that is greater than 1.0 shows that there is an increased risk among the people in Group A. • This means if the relative risk was 1.5, people in Group A would be 50% more likely than people in all other groups to die from a cause.
What does a relative risk of 2.8 mean?
Thus the relative risk of seizure when taking the specific medication is 2.8 (2.8 = 0.16 / 0.057). A person is 2.8 times more likely to have a seizure when taking the specific medication, but that is only a 0.103% increase in absolute risk (1 in 1000 increase in absolute risk).
What does a relative risk of 2.5 mean?
This means that. those in the control group were 2.5 times more likely to die than those in the treatment group. The relative risk is interpreted in terms of the risk of the group in the numerator.
What does an odds ratio of 0.4 mean?
For example, the odds ratio of 0.4 could mean, in numerical terms it means that for every 10 females without bowel cancer there are 20 who does, while in males, for every 10 individuals who do not have the tumor there are 50 who does”
How do you convert relative risk to absolute risk?
To calculate absolute risk from relative risk, you need to know the absolute risk for at least one of the groups. So if the relative risk for men of having X compared to women having X is 3, and you know the absolute risk of X in women is 1/100, then you know the absolute risk of having X in men is 3/100.
What is risk reduction factor?
Risk reduction factor can also be used to indicate the probability of failure for an instrumented function when the SIL mode is low demand. The risk reduction factor is the inverse of the required probability of failure, which is represented in years. For example, a required probability of failure value of .
What is relative risk reduction in statistics?
The relative risk reduction is the difference in event rates between two groups, expressed as a proportion of the event rate in the untreated group. For example, if 20% of patients die with treatment A, and 15% die with treatment B, the relative risk reduction is 25%.
What is relative risk reduction?
Relative risk reduction(RRR) tells you by how much the treatment reduced the risk of bad outcomes relative to the control group who did not have the treatment. In the previous example, the relative risk reduction of fever and rash in the group of the children on the interventionwas 40 per cent (1 – 0.6 = 0.4 or 40 per cent).
What is the RR of a group given intervention?
For technical reasons, some other measures are often used. The relative risk(RR) of a bad outcomein a group given interventionis a proportional measure estimating the size of the effect of a treatment compared with other interventions or no treatment at all. It is the proportion of bad outcomes in the intervention group divided by the proportion of bad outcomes in the control group. In this hypothetical case, the RR is 0.6 (12 per cent ÷ 20 per cent = 0.6).
How do you interpret the results of a randomised controlled trial?
How do you interpret the results of a randomised controlled trial? A common measure of a treatment is to look at the frequency of bad outcomes of a disease in the group being treated compared with those who were not treated. For instance, supposing that a well-designed randomised controlled trial in children with a particular disease found that 20 per cent of the control group developed bad outcomes, compared with only 12 per cent of those receiving treatment. Should you agree to give this treatment to your child? Without knowing more about the adverse effects of the therapy, it appears to reduce some of the bad outcomes of the disease. But is its effect meaningful?
What is the ARR in research?
Absolute riskreduction (ARR) – also called risk difference (RD) – is the most useful way of presenting research results to help your decision-making. In this example, the ARR is 8 per cent (20 per cent - 12 per cent = 8 per cent). This means that, if 100 children were treated, 8 would be prevented from developing bad outcomes. Another way of expressing this is the number needed to treat(NNT). If 8 children out of 100 benefit from treatment, the NNT for one child to benefit is about 13 (100 ÷ 8 = 12.5).
What happens when the RR is less than 1?
When a treatment has an RRgreater than 1, the riskof a bad outcomeis increased by the treatment; when the RR is less than 1, the risk of a bad outcome is decreased , meaning that the treatment is likely to do good. For example, when the RR is 2.0 the chance of a bad outcome is twice as likely to occur with the treatment as without it, whereas an RR of 0.5 means that the chance of a bad outcome is twice as likely to occur without the intervention. When the RR is exactly 1, the risk is unchanged. For example, a report may state ‘The relative risk of blindness in people given drug T was 1.5’. This shows that the drug increased the risk of blindness. Another measure that is used is the odds ratio. For practical purposes, assume that the odds ratio is the same as the relative risk. Sometimes the outcome is a good one and the interpretation of relative risk is the opposite of what we have just outlined.
Is the RRR the same as the ARR?
The RR(and therefore the RRR) is often the same in people irrespective of their level of risk, which means that the ARR will be greatest in those at greatest risk, as shown in Table 18.1. The greater your risk, the more you stand to gain from the intervention.
What is the absolute risk reduction of 2 in 20?
Say men have a 2 in 20 risk of developing a certain disease by the time they reach the age of 60. Then, say research shows that a new treatment reduces the relative risk of getting this disease by 50%. The 50% is the relative risk reduction, and is referring to the effect on the 2. 50% of 2 is 1. So this means that the absolute risk is reduced from from 2 in 20, to 1 in 20.
What would happen if the absolute risk of developing the disease was 4 in 100?
If the absolute risk of developing the disease was 4 in 100 then this 25% reduction in relative risk would reduce the absolute risk to 3 in 100. However, this can be looked at another way. If 100 people do not take the medicine, then 4 in those 100 people will get the disease.
What is absolute risk?
Absolute risk of a disease is your risk of developing the disease over a time period. We all have absolute risks of developing various diseases such as heart disease, cancer, stroke, etc. The same absolute risk can be expressed in different ways.
How much does new treatment reduce risk of X disease?
Treatments for medical conditions are often quoted in the press along the lines ... "New treatment reduces your risk of X disease by 25%". Whilst this sounds good, it usually refers to the relative risk. However, the benefit really depends on how common or rare the disease is.
Why are groups compared to others?
All sorts of groups are compared to others in medical research to see if belonging to a group increases or decreases your risk of developing certain diseases. For example, research has shown that smokers have a higher risk of developing heart disease compared to (relative to) non-smokers.
When deciding on whether to take a treatment, should you decide with your doctor?
When deciding on whether to take a treatment, ideally you should decide with your doctor if the reduction in the absolute risk outweighs the risks, side-effects and costs of treatment.
What is the NNT in medical research?
A figure which is often quoted in medical research is the NNT. This is the number of people who need to take the treatment for one person to benefit from the treatment .
What is relative risk?
Mathematically, it is the expressed as the incidence rate of the outcome in the exposed group,
How to interpret relative risk?
This way the relative risk can be interpreted in Bayesian terms as the posterior ratio of the exposure (i.e. after seeing the disease) normalized by the prior ratio of exposure. If the posterior ratio of exposure is similar to that of the prior, the effect is approximately 1, indicating no association with the disease, since it didn't change beliefs of the exposure. If on the other hand, the posterior ratio of exposure is smaller or higher than that of the prior ratio, then the disease has changed the view of the exposure danger, and the magnitude of this change is the relative risk.
What is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unex?
The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association between the exposure and the outcome.
What is the difference between logistic regression and Poisson regression?
In statistical modelling, approaches like Poisson regression (for counts of events per unit exposure) have relative risk interpretations: the estimated effect of an explanatory variable is multiplicative on the rate and thus leads to a relative risk. Logistic regression (for binary outcomes, or counts of successes out of a number of trials) must be interpreted in odds-ratio terms: the effect of an explanatory variable is multiplicative on the odds and thus leads to an odds ratio.
Why is odds ratio used in case control?
In practice the odds ratio is commonly used for case-control studies, as the relative risk cannot be estimated. In fact, the odds ratio has much more common use in statistics, since logistic regression, often associated with clinical trials, works with the log of the odds ratio, not relative risk.
When to use odds ratio?
In practice the odds ratio is commonly used for case-control studies, as the relative risk cannot be estimated.
Is apixaban a risk factor?
In this case, apixaban is considered to be a protective factor rather than a risk factor because it is associated with causing a reduced risk of disease. Assuming the causal effect between the exposure and the outcome, values of RR can be interpreted as follows: RR = 1 means that exposure does not affect the outcome.
What are some examples of high relative risk reduction?
It is found that the suit cuts lightning deaths so that for every 100 deaths by lightning in non-suit wearers there is only one death in suit wearers. This is an example of a high relative risk reduction (RRR). The absolute risk reduction (ARR) will be very small, however, because lightning strikes on people are very rare. In other words, wearing the suit changes an extremely small risk into an even smaller risk.
What is a RCT study?
These kinds of studies are usually randomized controlled trials ( RCTs), generally considered the gold standard in validating the effect of any medical intervention. With a RCT, the investigators are able to avoid many of the limitations and biases that are likely to occur with other research methods. However, results from a RCT are not problem-free and should be interpreted with caution. Here once again the implications of RRR and ARR must be understood.
What is the Pfizer study?
The Pfizer study includes a figure that compares the cumulative number of vaccinated patients that became ill versus the cumulative number of placebo patients that became ill. The graph looks similar to this:
Why is the ARR important?
Thus, the ARR is an important consideration when trying to answer the question of whether something is worth doing. We might even argue that the ARR is a vital consideration, particularly in issues of societal impact.
What does a relative risk of 1.0 mean?
A relative risk of 1.0 indicates no difference between comparison groups.
What is relative risk?
Relative risk, also known as risk ratio, is the risk of an event in the experimental group divided by that in the control group. For the sheepskin trial, this can be calculated from the data in Table 1 .
What is a Hazard Ratio?
Hazard ratio is a measure of relative risk over time in circumstances where we are interested not only in the total number of events, but in their timing as well. The event of interest may be death or it may be a non-fatal event such as readmission or symptom change.
How to appreciate clinical trial results?
To appreciate the significance of clinical trial results, clinicians need to understand the mathematical language used to describe treatment effects. When comparing intervention and control groups in a trial, results may be reported in terms of relative or absolute risk (or probability), or as more statistically sophisticated entities based on odds ...
What is absolute risk reduction?
Absolute risk reduction, also termed risk difference, is the difference between the absolute risk of an event in the intervention group and the absolute risk in the control group.
What is a 95% confidence interval?
The confidence interval represents the range of values within which we are 95% confident that the true population estimate lies. If the number of events such as death occurring over time is fairly small (as occurs with small samples and/or low case fatality rate), then the precision with which the true probability of the event can be estimated is relatively low, as reflected in wider confidence intervals. Narrower confidence intervals indicate more precise results. The 95% confidence intervals represent almost two standard deviations around the mean.
What Are Absolute and Relative Risks?
Number Needed to Treat
- A figure which is often quoted in medical research is the NNT. This is the number of people who need to take the treatment for one person to benefit from the treatment. For example, say a pharmaceutical company reported that medicine X reduced the relative risk of developing a certain disease by 25%. If the absolute risk of developing the disease was 4 in 100 then this 25…
Helping to Decide About Taking A Treatment
- The decision on whether to take a treatment needs to balance various things, such as: 1. What is the absolute risk of getting the disease to start with? 2. How serious is the disease anyway? 3. How much is the absolute risk reduced with treatment? 4. What are the risks or side-effects in taking the treatment? 5. How much does the treatment cost? Is it worth it to an individual if the i…
in Summary
- Treatments for medical conditions are often quoted in the press along the lines ... "New treatment reduces your risk of X disease by 25%". Whilst this sounds good, it usually refers to the relativerisk. However, the benefit really depends on how common or rare the disease is. A large reduction of relative risk for a rare disease might not mean much...
Overview
The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association between the exposure and the outcome.
Comparison to the odds ratio
The relative risk is different from the odds ratio, although the odds ratio asymptotically approaches the relative risk for small probabilities of outcomes. If IE is substantially smaller than IN, then IE/(IE + IN) IE/IN. Similarly, if CE is much smaller than CN, then CE/(CN + CE) CE/CN. Thus, under the rare disease assumption
Statistical use and meaning
Relative risk is used in the statistical analysis of the data of ecological, cohort, medical and intervention studies, to estimate the strength of the association between exposures (treatments or risk factors) and outcomes. Mathematically, it is the incidence rate of the outcome in the exposed group, , divided by the rate of the unexposed group, . As such, it is used to compare the risk of an adverse outcome when receiving a medical treatment versus no treatment (or placebo…
Usage in reporting
Relative risk is commonly used to present the results of randomized controlled trials. This can be problematic if the relative risk is presented without the absolute measures, such as absolute risk, or risk difference. In cases where the base rate of the outcome is low, large or small values of relative risk may not translate to significant effects, and the importance of the effects to the public health can be overestimated. Equivalently, in cases where the base rate of the outcome i…
Bayesian interpretation
We could assume a disease noted by , and no disease noted by , exposure noted by , and no exposure noted by . The relative risk can be written as
This way the relative risk can be interpreted in Bayesian terms as the posterior ratio of the exposure (i.e. after seeing the disease) normalized by the prior ratio of exposure. If the posterior ratio of exposure is similar to that of the prior, the effect is approximately 1, indicating no associ…
See also
• Cochran–Mantel–Haenszel statistics for aggregation of risk ratios across several strata
• Population impact measure
• OpenEpi
• Rate ratio
External links
• Relative risk online calculator