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How does odds ratio compare to probability?

Odds are the probability of an event occurring divided by the probability of the event not occurring. An odds ratio is the odds of the event in one group, for example, those exposed to a drug, divided by the odds in another group not exposed. Odds ratios always exaggerate the true relative risk to some degree.
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How do odds compare to probability?

The distinction is simple: The probability that an event will occur is the fraction of times you expect to see that event in many trials. Probabilities always range between 0 and 1. The odds are defined as the probability that the event will occur divided by the probability that the event will not occur.
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What does odds ratio mean in probability?

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.
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Why do we use probability instead of odds ratio?

A probability must lie between 0 and 1 (you cannot have more than a 100% chance of something). Odds are not so constrained. Odds can take any positive value (e.g. a ⅔ probability is the same as odds of 2/1). If instead we use odds (actually the log of odds, or logit), a linear model can be fit.
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What does an odds ratio of 0.99 mean?

Odds ratios between 0 and 0.99 indicate a lower risk, between 1 and infinity indicate a higher risk, and equal to 1 indicate no relationship between two variables.
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Relative Risk & Odds Ratios

What does an odds ratio of 0.92 mean?

For example, the odds ratio (OR) for age is 0.92. Thus, we could calculate: Change in Odds %: (0.92 – 1) * 100 = -8% This means that each additional increase of one year in age is associated with an 8% decrease in the odds of a mother having a healthy baby.
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What does an odds ratio of 0.80 mean?

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). RRR is usually constant across a range of absolute risks. But the ARR is higher and the NNT lower in people with higher absolute risks.
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Do odds reflect probabilities?

The odds on display never reflect the true probability or chance of an event occurring (or not occurring).
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What is the relationship between odds ratio and p value?

If the p-value for your odds ratio is less than your significance level (e.g., 0.05), reject the null hypothesis. The interpretation is that difference between your sample's odds ratio and one is statistically significant.
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What is the difference between odds ratio and probability in logistic regression?

In a logistic regression model, odds ratio provide a more coherent solution as compared to probabilities. Odds ratio represent the constant effect of an independent variable on a dependent variable. Here, being constant means that this ratio does not change with a change in the independent (predictor) variable.
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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.
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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).
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Does higher odds mean higher probability?

Odds tell you how likely an event is to happen

Betting odds are a way to represent the probability/likelihood of an event occurring. Who will win Eurovision Song Contest? The lower the odds for a participant are, the more likely is it that the participant will win Eurovision.
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What does an odds ratio of 0.05 mean?

An alpha of 0.05 means the confidence interval is 95% (1 – alpha) the true odds ratio of the overall population is within range. A 95% confidence is traditionally chosen in the medical literature (but other confidence intervals can be used).
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Does odds ratio indicate risk?

The odds ratio (OR) is the ratio of odds of an event in one group versus the odds of the event in the other group. An RR (or OR) of 1.0 indicates that there is no difference in risk (or odds) between the groups being compared.
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Is probability basically the odds of something happening?

Probability is simply how likely something is to happen. Whenever we're unsure about the outcome of an event, we can talk about the probabilities of certain outcomes—how likely they are. The analysis of events governed by probability is called statistics.
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How accurate is probability?

Furthermore, probability is not predictability. Knowing that that the probability that a fair coin will land on heads is 50%, you in no way can accurately predict the next flip. Maybe you can predict on average how many flips out of 100 will be heads, but you won't be able to predict the next flip with any certainty.
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Does probability tell us exactly what happens?

Probability is a measure of the likelihood of an event to occur. Many events cannot be predicted with total certainty. We can predict only the chance of an event to occur i.e., how likely they are going to happen, using it.
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What is considered a strong odds ratio?

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) ...
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How do you interpret 0.15 odds ratio?

Because it is an OR, we must say that for every 0.15 (or 15) persons who experience the event in the experimental group, 1 person (or 100 persons) will experience the event in the control group. That is, the odds are 15 to 100.
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What is ideal odds ratio?

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. The odds ratio must be nonnegative if it is defined.
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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.
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What does an odds ratio of 0.65 mean?

The odds ratio (OR) is 0.65. We can state that the odds for infection are lower in the treatment group, since the value is less than 1.0. If we subtract the OR from 1.0 and multiply the result by 100%, we get a percentage reduction in odds, which is 34.8%.
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