What is odds ratio in simple terms?

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.

What does odds ratio tell you?

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.

What is odds ratio with example?

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 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).

What does an odds ratio of 2.0 mean?

Here it is in plain language. An OR of 1.2 means there is a 20% increase in the odds of an outcome with a given exposure. An OR of 2 means there is a 100% increase in the odds of an outcome with a given exposure. Or this could be stated that there is a doubling of the odds of the outcome.

Odds Ratio Explained - Chocolate Consumption and Cardiovascular Disease

What happens if 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 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 a low odds ratio mean?

A low odds ratios indicates that the factor under examination is associated with a decrease, rather than an increase of risk relating to your outcome measure. Any significant departure from an odds ratio of 1 is of interest in understanding a factor's impact on outcomes.

Is The odds ratio positive OR negative?

To conclude, the important thing to remember about the odds ratio is that an odds ratio greater than 1 is a positive association (i.e., higher number for the predictor means group 1 in the outcome), and an odds ratio less than 1 is negative association (i.e., higher number for the predictor means group 0 in the outcome ...

Does odds ratio tell you risk?

The odds ratio can also be used to determine whether a particular exposure is a risk factor for a particular outcome, and to compare the magnitude of various risk factors for that outcome.

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.

What is the difference between odds and rate ratio?

Rate is the number of new cases that occur per the total amount of time a person is at risk of becoming a case. It is expressed as person-time such as 17.8 cases per 100 person years. Odds is the likelihood of a new case occurring rather than not occurring.

What if odds ratio is 0?

If you have an infinite odds in the denominator, then your odds ratio is zero. Finally, if you have a zero odds in the denominator, then your odds ratio is infinite. The only case you can't handle is when both groups have 100% survival or 0% survival. This forces you to divide infinity by infinity or zero by zero.

What are the disadvantages of odds ratio?

The odds ratio will always overstate the case when interpreted as a relative risk, and the degree of overstatement will increase as both the initial risk increases and the size of any treatment effect increases.

Is it better to have high OR low odds?

Odds is the payout of a winning bet

Odds show how much money you will win, if you bet on an event to happen. The higher the odds are, the more you will win, relative to your stake.

Are lower odds better OR worse?

Remember that lower odds return a higher profit.

Betting on the underdog is riskier than betting on a favorite, but a higher risk means a higher potential reward. The "longer the odds," or the less likely, the more money you could win.

Which odds ratio is strongest?

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 does an odds ratio of 0.1 mean?

From probability to odds

So a probability of 0.1, or 10% risk, means that there is a 1 in 10 chance of the event occurring.

What does an odds ratio of 0.91 mean?

In general the relationship between a factor increase and the percentage change is (f - 1) * 100%. So an odds ratio of 0.91 corresponds to a (0.91 - 1)*100% = -9% change in odds for a unit increase in factor B, or a 9% decrease in the odds for a unit change in factor B.

What does an odds ratio of .75 mean?

"When you are interpreting an odds ratio (or any ratio for that matter), it is often helpful to look at how much it deviates from 1. So, for example, an odds ratio of 0.75 means that in one group the outcome is 25% less likely. An odds ratio of 1.33 means that in one group the outcome is 33% more likely."

Why is odds ratio negative?

Positive odds ratios indicate that the event is more likely to occur, whilst negative odd ratios indicate the event is less likely to occur.

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.

When can odds ratios mislead?

Substantial discrepancies between the odds ratio and the relative risk are seen only when the effect sizes are large and the initial risk is high.

Can odds ratio be over 100%?

Probability values can only range from 0 to 1 (0% to 100%), whereas odds can take on any value.

How do you report odds ratio?

The odds are the ratio of the probability that an outcome occurs to the probability that the outcome does not occur. For example, sup- pose that the probability of mortality is 0.3 in a group of patients. This can be expressed as the odds of dying: 0.3/(1 − 0.3) = 0.43.