Why is odds ratio better than 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.

Why is odds ratio greater than relative risk?

The basic difference is that the odds ratio is a ratio of two odds (yep, it's that obvious) whereas the relative risk is a ratio of two probabilities. (The relative risk is also called the risk ratio).

Why use odds ratio and not 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).

What is the advantage of odds ratio?

The great value of the odds ratio is that it is simple to calculate, very easy to interpret, and provides results upon which clinical decisions can be made. Furthermore, it is sometimes helpful in clinical situations to be able to provide the patient with information on the odds of one outcome versus another.

Why is odds ratio used in case-control studies instead of relative risk?

The key difference being, for odds ratio, one needs to know the conditional probabilities P(I|N),P(C|N), which are known in case control studies; whereas for relative risk, P(I),P(C) are not known from a retrospective study design. Cool!

Medical Statistics - Part 7: OR and RR in Observational Studies

Why is odds ratio best for case-control?

The odds ratio tells us how much higher the odds of exposure are among case-patients than among controls. An odds ratio of • 1.0 (or close to 1.0) indicates that the odds of exposure among case-patients are the same as, or similar to, the odds of exposure among controls. The exposure is not associated with the disease.

Is odds ratio a good approximation of relative risk?

It is not true in all situations. The odds ratio only gives an estimate of the relative risk if the outcome is a low probability outcome. (Same insight as Poisson approximation to the binomial distribution).

When should odds ratio be used?

Odds ratios frequently are used to present strength of association between risk factors and outcomes in the clinical literature. Odds and odds ratios are related to the probability of a binary outcome (an outcome that is either present or absent, such as mortality).

What is an example of relative risk and odds ratio?

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).

Why not relative risk for case control?

Another popular textbook states, “relative risks cannot be calculated directly from a case-control study,” because case-control studies obtain only an “estimate of relative risks based on the odds ratios that are obtained in the case-control studies” (5, p. 208).

How do you describe odds ratio in words?

Odds Ratio (OR) is a measure of association between 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.

How do you convert odds ratio to relative risk?

To convert an odds ratio to a risk ratio, you can use "RR = OR / (1 – p + (p x OR)), where p is the risk in the control group" (source: http://www.r-bloggers.com/how-to-convert-odds-ratios-to-relative-risks/).

When can you not use relative risk?

In a case-control study, you cannot measure incidence, because you start with diseased people and non-diseased people, so you cannot calculate relative risk.

Why is relative risk misleading?

Relative risk, sometimes called the risk ratio, is good for showing the difference between two groups but can be misleading as it is independent of the original number of cases. For example, if you had: 100 people on a drug and 1 had a heart attack = 1% risk of heart attack.

What is the disadvantage of relative risk?

Nevertheless, the sole reporting of relative risks has a major drawback, because it may obscure the magnitude of the effect of an intervention. When relative risks are used for the presentation of effects of a treatment, this can make the treatment seem better than it actually is.

Is relative risk generally smaller than odds ratio?

The figures show that the odds ratio will always exaggerate the size of the effect compared with a relative risk. 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.

What is odds ratio in statistics for dummies?

Odds Ratio is a measure of the strength of association with an exposure and an outcome. OR > 1 means greater odds of association with the exposure and outcome. OR = 1 means there is no association between exposure and outcome. OR < 1 means there is a lower odds of association between the exposure and outcome.

How do you describe odds ratio in a paper?

There are two ways to describe an odds ratio. One is simply “OR times the odds.” The other is as a (OR-1)*100% increase.

What is odds ratio simple?

A measure of the odds of an event happening in one group compared to the odds of the same event happening in another group.

Are relative risks meaningless?

Relative risks are often reported in newspaper headlines, but without the context of absolute (or baseline) risk, this information is meaningless.

Which relative risk is better?

The relative benefit is 1 – relative risk. 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.

Can relative risk RR be estimated by odds ratio OR in a case-control study?

As a result, risks, rates, risk ratios or rate ratios cannot be calculated from the typical case-control study. However, you can calculate an odds ratio and interpret it as an approximation of the risk ratio, particularly when the disease is uncommon in the population.

Where is odds ratio used?

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).

What is odds ratio OR relative risk in clinical trials?

Background and objectives: In clinical trials, the relative risk or risk ratio (RR) is a mainstay of reporting of the effect magnitude for an intervention. The RR is the ratio of the probability of an outcome in an intervention group to its probability in a control group.

Does relative risk tell you nothing about actual risk?

Relative risk measures how much more likely one group is to experience an outcome than another, but without knowing the baseline or absolute risk, it says nothing about your actual risk. People's perception of risk can change depending on how statistics are presented- as decimals, percentages, fractions, or graphs.