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When to use odds ratio and relative risk

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When to Use Odds Ratio and Relative Risk: A Comprehensive Guide

Understanding the concepts of odds ratio and relative risk is crucial in statistical analysis, especially in medical and epidemiological research. This brief review aims to highlight the positive aspects of using odds ratio and relative risk, providing a clear understanding of when and how to use these measures.

I. Definition and Explanation:

  1. Odds Ratio:

    • Definition: The odds ratio measures the association between an exposure and an outcome in a case-control study.
    • Positive Aspects:

      • Helpful in studies with rare outcomes.
      • Allows for the estimation of odds in retrospective studies.
      • Easy interpretation: an odds ratio of 1 suggests no association, while an odds ratio greater than 1 indicates a positive association, and an odds ratio less than 1 suggests a negative association.
  2. Relative Risk:

    • Definition: The relative risk measures the association between an exposure and an outcome in a cohort study.
    • Positive Aspects:

      • Provides direct estimates of risk.
      • Suitable for prospective studies.
      • Simple interpretation: a relative risk of 1 suggests no association, while a relative risk greater than 1 indicates an increased risk, and a relative risk less than 1 suggests
Odds ratios are most commonly used in case-control studies, however they can also be used in cross-sectional and cohort study designs as well (with some modifications and/or assumptions).

Do you use odds ratio OR relative risk in case-control study?

Key Concept: In a study that is designed and conducted as a case-control study, you cannot calculate incidence. Therefore, you cannot calculate risk ratio or risk difference. You can only calculate an odds ratio. However, in certain situations a case-control study is the only feasible study design.

How can you determine whether an odds ratio OR relative risk is statistically significant using a confidence interval?

RR values are accompanied by their 95% confidence intervals (CIs). The statistical significance of an RR value can be inferred from the 95% CI. 8 If the CI includes the value 1.00, the RR is not statistically significant.

What is the difference between likelihood ratio and odds ratio?

The odds ratio is the effect of going from “knowing the test negative” to “knowing it's positive” whereas the likelihood ratio + is the effect of going from an unknown state to knowing the test is +.

Why do we use odds ratio over relative risk?

When the outcome is not rare in the population, if the odds ratio is used to estimate the relative risk it will overstate the effect of the treatment on the outcome measure. The odds ratio will be greater than the relative risk if the relative risk is greater than one and less than the relative risk otherwise.

When an odds ratio is used to approximate the relative risk?

When the risks (or odds) in the two groups being compared are both small (say less than 20%) then the odds will approximate to the risks and the odds ratio will approximate to the relative risk.

Why do we use odds ratio for case control?

In these case-control studies, the odds ratio provides a valid estimate of the risk ratio without assuming that the disease is rare in the source population.

Frequently Asked Questions

What are the advantages of odds ratio?

Another nice feature of odds ratios from a logistic regression is that it is easy to test the statistical strength of association. The stan- dard test is whether the parameter (log odds) equals 0, which cor- responds to a test of whether the odds ratio equals 1.

What is the difference between odds ratio and likelihood ratio?

The odds ratio is the effect of going from “knowing the test negative” to “knowing it's positive” whereas the likelihood ratio + is the effect of going from an unknown state to knowing the test is +.

When can the risk ratio be approximated by the odds ratio?

When the risks (or odds) in the two groups being compared are both small (say less than 20%) then the odds will approximate to the risks and the odds ratio will approximate to the relative risk.

Is relative risk the same as rate ratio?

Risk ratio: ratio of the risk of an event in one group (exposure or intervention) to that in another group (control). So it depends on your definitions of rate and risk. The term "relative risk" is sometimes used as a synonym for risk ratio, and rate ratio is one of the relative risk measures too.

In which kind of study should you use odds ratio instead of the relative risk?

In case-control studies, and in cohort studies in which the outcome occurs in less than 10% of the unexposed population, the OR provides a reasonable approximation of the RR. However, when an outcome is common (iY 10% in the unexposed group), the OR will exaggerate the RR.

When an odds ratio is used to estimate the relative risk quizlet?

When can OR be used to estimate RR? The odds ratio always approximates the relative risk if the disease is frequent. In a cohort study of obesity and myocardial infarction, the odds ratio was calculated to be 4.5 while the relative risk was 2.5.

Can you use odds ratio to estimate risk ratio?

When a study outcome is rare in all strata used for an analysis, the odds ratio estimate of causal effects will approximate the risk ratio; therefore, odds ratios from most case-control studies can be interpreted as risk ratios.

FAQ

Should I use odds ratio OR relative risk?
Odds ratios (OR) are commonly reported in the medical literature as the measure of association between exposure and outcome. However, it is relative risk that people more intuitively understand as a measure of association. Relative risk can be directly determined in a cohort study by calculating a risk ratio (RR).
How do you know when to use odds ratio?
When is it used? Odds ratios are used to compare the relative odds of the occurrence of the outcome of interest (e.g. disease or disorder), given exposure to the variable of interest (e.g. health characteristic, aspect of medical history).
Why do we use relative risk?
Thus relative risk provides an increase or decrease in the likelihood of an event based on some exposure. Relative risk has the benefit of being a ratio of risks which means it can be applied to populations with differing disease prevalence. Relative risk does not specify the absolute risk of the event occurring.
When should I use odds ratio?
Odds ratios are most commonly used in case-control studies, however they can also be used in cross-sectional and cohort study designs as well (with some modifications and/or assumptions).
Which measure is more appropriate in this design the relative risk or odds ratio?
Odds ratio is calculated for case control studies, while relative risk is for cohort studies, so it depends on the study design. Odds ratio is for case control studies and relative risk for cohort studies.
Can risk ratio and odds ratio be the same?
RELATIONSHIP OF RISK RATIO AND ODDS RATIO When there is no association between exposure and outcome, both OR and RR are identical and equal to 1.0 [Table 3a]. When there is an association between an exposure and an outcome, OR exaggerates the estimate of their relationship (is farther from 1.0 than RR).
How do you interpret odds ratio and risk ratio?
The odds ratio is interpreted in the same manner as the risk ratio or rate ratio with an OR of 1.0 indicating no association, an OR greater than 1.0 indicating a positive association, and an OR less than 1.0 indicating a negative, or protective association.

When to use odds ratio and relative risk

What does it mean when the odds ratio is equal to one? An odds ratio of 1 indicates that the condition or event under study is equally likely to occur in both groups. An odds ratio greater than 1 indicates that the condition or event is more likely to occur in the first group.
Why are the relative risk and odds ratio approximately equal? When the risks (or odds) in the two groups being compared are both small (say less than 20%) then the odds will approximate to the risks and the odds ratio will approximate to the relative risk.
What is an example of odds ratio and relative risk? Thus in our example, the odds ratio is 20.5 (smokers have 20 times the odds of having lung cancer than non-smoker); whereas the relative risk is 17 (smokers have 17 times the relative risk to have lung cancer than non-smokers).
What does a higher odds ratio indicate? Important points about Odds ratio: OR >1 indicates increased occurrence of an event. OR <1 indicates decreased occurrence of an event (protective exposure) Look at CI and P-value for statistical significance of value (Learn more about p values and confidence intervals here) In rare outcomes OR = RR (RR = Relative Risk)
Why is odds ratio used in case-control studies instead of relative risk? In these case-control studies, the odds ratio provides a valid estimate of the risk ratio without assuming that the disease is rare in the source population.
What is odds ratio versus likelihood ratio? The odds ratio is the effect of going from “knowing the test negative” to “knowing it's positive” whereas the likelihood ratio + is the effect of going from an unknown state to knowing the test is +.
Is odds ratio always larger than risk ratio? That is, if the odds ratio is less than one then it is always smaller than the relative risk. Conversely, if the odds ratio is greater than one then it is always bigger than the relative risk.
  • How do you know if a relative risk is statistically significant?
    • Any RR > 2 is statistically-significant when N*P1 is at least 10. Any RR > 1.6 is statistically-significant when N*P1 is at least 25. As the count in the smallest cell decreases, the Normal Approximation becomes less adequate.
  • How do you interpret relative risk less than 1?
    • A relative risk of one implies there is no difference of the event if the exposure has or has not occurred. If the relative risk is greater than 1, then the event is more likely to occur if there was exposure. If the relative risk is less than 1, then the event is less likely to occur if there was exposure.
  • What does a relative risk of 2.5 mean?
    • 0.1 = 2.5. 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 odds ratio determine?
    • What is an odds ratio? An odds ratio (OR) is a measure of association between an exposure and an outcome. The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure.
  • Do you use odds ratio or relative risk in case-control study?
    • Key Concept: In a study that is designed and conducted as a case-control study, you cannot calculate incidence. Therefore, you cannot calculate risk ratio or risk difference. You can only calculate an odds ratio. However, in certain situations a case-control study is the only feasible study design.
  • How can you determine whether an odds ratio or relative risk is statistically significant using a confidence interval?
    • RR values are accompanied by their 95% confidence intervals (CIs). The statistical significance of an RR value can be inferred from the 95% CI. 8 If the CI includes the value 1.00, the RR is not statistically significant.