Are odds ratios misleading?

Interpreting an odds ratio as a relative risk is a common mistake in the medical literature. The odds ratio is a good proxy of the relative risk when the probability of the event is low. However, compared with the relative risk, the odds ratio always exaggerates the size of the effect to some degree.

Why can odds ratios be misleading?

The discrepancy between a relative risk reduction and the equivalent relative odds reduction (100×(1−odds ratio)%) can be misleading. When event rates are high (commonly the case in trials and systematic reviews) the relative odds reduction can be many times larger than the equivalent relative risk reduction.

Are odds ratios reliable?

Although large discrepancies between the odds ratio and the relative risk are possible, the odds ratio overstates the relative risk by less than 50% for a wide range of both initial risks and effect sizes.

Are odds ratios biased?

Bias in the risk ratio, rate ratio, or odds ratio can be produced even if measured errors are equal between exposed and unexposed or between study participants that have or do not have the health outcome.

Are odds ratios predictive?

The interpretation of the odds ratio depends on whether the predictor is categorical or continuous. Odds ratios that are greater than 1 indicate that the event is more likely to occur as the predictor increases. Odds ratios that are less than 1 indicate that the event is less likely to occur as the predictor increases.

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

Is it better to use odds ratio OR 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.

Is The odds ratio significant?

Statistical Significance

If an odds ratio (OR) is 1, it means there is no association between the exposure and outcome. So, if the 95% confidence interval for an OR includes 1, it means the results are not statistically significant.

What is the odds ratio paradox?

The odds ratio paradox relates to three chained proportions com- pared between the same two groups, and involves the magnitude, but not the direction of the effect.

What is the rule of thumb for odds ratio?

But how big an effect is it? Epidemiologists use this very rough rule of thumb: An odds ratio of 4 or more is pretty strong and not likely to be able to be explained away by some unmeasured variables. An odds ratio bigger than 2 and less than 4 is possibly important and should be looked at very carefully.

What is the odds ratio for dummies?

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.

What happens if odds ratio crosses 1?

Most studies report the 95% confidence interval (95%CI). If the confidence interval crosses 1 (e.g. 95%CI 0.9-1.1) this implies there is no difference between arms of the study.

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 +. “Unknown state” is not always well defined so I stick to logistic regression for the diagnostic problem.

Why use odds ratio not risk ratio?

“Risk” refers to the probability of occurrence of an event or outcome. Statistically, risk = chance of the outcome of interest/all possible outcomes. The term “odds” is often used instead of risk. “Odds” refers to the probability of occurrence of an event/probability of the event not occurring.

Are odds ratios ever negative?

The odds ratio is always positive, although the estimated log odds can be positive or negative (log odds of −0.2 equals odds ratio of 0.82 = exp(−0.2)).

What is the difference between odds ratio and absolute risk?

The absolute risk is the probability of an event in a sample or population of interest. The relative risk (RR) is the risk of the event in an experimental group relative to that in a control group. The odds ratio (OR) is the odds of an event in an experimental group relative to that in a control group.

Is odds ratio the same as correlation?

Odds ratio and correlation don't measure the same thing- correlation looks at how much one variable is explained by another (for example, is how much is wieght explaine by height?). Odds ratio compare the odds of a specific outcome in two groups, one exposied an done unexposed to a specific exposure.

Is odds ratio the same as hazard?

Hazard ratios differ from relative risks (RRs) and odds ratios (ORs) in that RRs and ORs are cumulative over an entire study, using a defined endpoint, while HRs represent instantaneous risk over the study time period, or some subset thereof.

What does an odds ratio of 0.8 mean?

Examples. RR of 0.8 means an RRR of 20% (meaning a 20% reduction in the relative risk of the specified outcome in the treatment group compared with the control group).

What does an odds ratio of 1.5 mean?

It means that the odds of a case having had exposure #1 are 1.5 times the odds of its having the baseline exposure. This is not the same as being 1.5 times as probable: odds are not the same as probability (odds of 2:1 against means a probability of 13).

Is odds ratio times more likely?

Definition in terms of group-wise odds

An odds ratio greater than 1 indicates that the condition or event is more likely to occur in the first group. And an odds ratio less than 1 indicates that the condition or event is less likely to occur in the first group.

How do you explain odds ratio to patients?

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.

What does it mean when odds ratio is less than 1?

If a predictor variable in a logistic regression model has an odds ratio less than 1, it means that a one unit increase in that variable is associated with a decrease in the odds of the response variable occurring.

What is the correct way to calculate an odds ratio?

The odds ratio is calculated by dividing the odds of the first group by the odds in the second group. In the case of the worked example, it is the ratio of the odds of lung cancer in smokers divided by the odds of lung cancer in non-smokers: (647/622)/(2/27)=14.04.

What does it mean when odds ratio == 1?

An odds ratio of less than 1 implies the odds of the event happening in the exposed group are less than in the non-exposed group. An odds ratio of exactly 1 means the odds of the event happening are the exact same in the exposed versus the non-exposed group.

What does an odds 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.