How to interpret risk ratios?
How to Interpret Risk Ratios: Since the relative risk is a simple ratio, errors tend to occur when the terms "more" or "less" are used. Because it is a ratio and expresses how many times more probable the outcome is in the exposed group, the simplest solution is to incorporate the words "times the risk" or "times as high as" in your interpretation.
What are odds ratios and risk ratios?
Risk ratios, odds ratios, and hazard ratios are three ubiquitous statistical measures in clinical research, yet are often misused or misunderstood in their interpretation of a study’s results [1].
What is the eponymous risk ratio (RR)?
This calculation - a ratio of two risks - is what is meant by the eponymous risk ratio (RR) statistic, also known as relative risk. It allows a specific number to be given for how much more risk an individual in one category bears compared to an individual in another category.
What is the relationship between incidence rate and risk ratio?
Rate ratios are closely related to risk ratios, but they are computed as the ratio of the incidence rate in an exposed group divided by the incidence rate in an unexposed (or less exposed) comparison group. Consider an example from The Nurses' Health Study.
What does a risk ratio of less than 1 indicate?
A risk ratio less than 1.0 indicates a decreased risk for the exposed group, indicating that perhaps exposure actually protects against disease occurrence.
What does a risk ratio of 0.5 mean?
An odds ratio of 0.5 would mean that the exposed group has half, or 50%, of the odds of developing disease as the unexposed group. In other words, the exposure is protective against disease.
What does a risk ratio of 0.75 mean?
2c) A risk ratio of 0.75 means there is an inverse association, i.e. there is a decreased risk for the health outcome among the exposed group when compared with the unexposed group. The exposed group has 0.75 times the risk of having the health outcome when compared with the unexposed group.
What does a risk ratio of 0.2 mean?
An OR of 0.2 means there is an 80% decrease in the odds of an outcome with a given exposure.
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.
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 1.25 mean?
Example of a relative risk This statistic is a relative risk (the relative risk is 1.25). It means inactive women are 25 percent more likely to develop breast cancer than women who exercise.
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”
What does a risk ratio above 1 mean?
A risk ratio of greater than one or of less than one usually means that being exposed to a certain substance or factor either increases (risk ratio greater than one) or decreases (risk ratio less than one) the risk of cancer, or that the treatments being compared do not have the same effects. Also called relative risk.
What does an odds ratio of 0.7 mean?
protective effectIf the Odds ratio is 0.7 then it indicates a protective effect - I.e a reduced odds of exposure in case vs control group. That reduced risk is 1-odds so will be 30 percent reduced risk fo exposure.
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 a relative risk of 1 mean?
A relative risk of one means there is no difference between two groups in terms of their risk of cancer, based on whether or not they were exposed to a certain substance or factor, or how they responded to two treatments being compared.
How are rate ratios related to risk ratios?
Rate ratios are closely related to risk ratios, but they are computed as the ratio of the incidence rate in an exposed group divided by the incidence rate in an unexposed (or less exposed) comparison group.
What does risk ratio mean?
In general: If the risk ratio is 1 (or close to 1), it suggests no difference or little difference in risk (incidence in each group is the same). A risk ratio > 1 suggests an increased risk of that outcome in the exposed group. A risk ratio < 1 suggests a reduced risk in the exposed group.
When to use "more" or "less" in relative risk?
Since the relative risk is a simple ratio, errors tend to occur when the terms "more" or "less" are used. Because it is a ratio and expresses how many times more probable the outcome is in the exposed group, the simplest solution is to incorporate the words "times the risk" or "times as high as" in your interpretation.
What is the risk ratio of vitamins C and E?
When subjects who took both vitamins were compared to those who took not vitamins at all, the risk ratio was found to be 0.70.
What is the endpoint of a randomized clinical trial?
In a randomized clinical trial (RCT) with a binary endpoint Y it is traditional in a frequentist analysis to summarize the estimated treatment effect with an odds ratio (OR), risk ratio (RR), or risk difference (RD, also called absolute risk reduction). For any of these measures there are several forms of estimation:
Is marginal adjusted estimate robust?
Marginal adjusted estimates may be robust, but may not accurately estimate RD for either any patient in the RCT or for the clinical population to which RCT results are to be applied, because in effect they assume that the RCT sample is a random sample from the clinical population, something not required and never realized for RCTs.
1. Introduction
Risk ratios are often recommended for summarizing the relationship between a covariate and an outcome in epidemiology [ 1 – 10 ]. They are simple and easy to compute [ 11 – 13 ], and when outcomes may exhibit correlation within clusters, ‘robust’ standard errors are available [ 10, 14 ].
2. Setting
Consider a collection of clusters (e.g. households, workplaces, villages), with ni subjects in cluster i. Let Yij ( t) be the binary indicator of infection for subject j in cluster i on or before time t ≥ 0. Let Ti be the time at which outcomes in cluster i are observed and recorded by researchers.
3. Results
We first consider a simple parametric version of ( 2.4) with two-person clusters and balanced covariate values for which a variety of precise analytic results can be derived.
4. Discussion
We have applied a standard and widely accepted measure of association to outcomes generated by a canonical stochastic model of infectious disease contagion.
Data accessibility
This paper uses only simulated data.
Authors' contributions
O.M., T.C. and F.W.C. conceived and designed the study and reviewed and revised the paper and gave final approval for publication. O.M. and F.W.C. derived the technical results. O.M. wrote the simulation code, conducted the simulations and wrote the majority of the paper.
Funding
This work was supported by grants R36 DA042643 from NIDA, R01 DA015612 from NIDA, DP2 OD022614 from NICHD, R01 AI112438-03 from NIAID, the Yale Center for Clinical Investigation, and the Center for Interdisciplinary Research on AIDS. Computing support was provided by the Yale Center for Research Computing and the W. M.