# How to Read the Odds Ratio

When you hear or see the words ‘odds ratio’ or ‘risk’, this probably means something to you: you’ve been told that you have a certain condition; or you’ve been offered a certain treatment and tested positive for that condition; or you’re interested in a certain area of medicine and want to learn more about it.

This ratio, also known as the ‘hazard ratio’, ‘risk ratio’, or ‘ratio of odds’, is a measure of the relationship between two (or more) things. In medicine, it’s often used to compare the likelihood of a problem occurring based on several factors. For example, let’s say you’re interested in comparing the risk of developing heart disease in people who smoke vs non-smokers. You can look at various risk factors such as gender, age, ethnicity, and family history and measure the odds of developing heart disease in each case.

If you’re a non-smoker, your odds of developing heart disease are 1 in 10. If you’re a female, non-smoker, and in your thirties, you have an odds ratio of 22.7 for heart disease. That means that, compared to a non-smoker in their thirties, your odds of developing heart disease are 22.7 times greater if you’re a female and non-smoker.

Now, say you’re interested in comparing the risk of developing liver cancer in people who drink alcohol vs non-drinkers. You can look at various risk factors such as gender, ethnicity, and family history and measure the odds of developing liver cancer in each case. If you’re a non-drinker, your odds of developing liver cancer are 1 in 16. If you’re a white man in your fifties, your odds are 1 in 6. If you’re a woman and non-drinker, your odds are 1 in 14. And if you have a family history of liver cancer, your odds are 1 in 4.

So, what does all this mean? Well, first off, you should know what an odds ratio is and how to read it. If you don’t, now’s a good time to learn. Second, know that it’s often used in medical research and can be a helpful tool in making decisions about your health. Last, just because a study uses an odds ratio doesn’t mean that it’s trying to tell you that smoking is safe than drinking alcohol. It could mean that the study found that, compared to non-smokers, the risk of alcohol-related problems increased 22.7 times in females and 1.7 times in males who smoked. This is just one example of what an odds ratio could mean. It’s not intended to be taken as medical advice, but as a guide to help you understand the study results better.

## How to Read the Odds Ratio

If you’re looking at a study that used an odds ratio to compare the likelihood of something occurring, like developing a disease or condition, you can follow the same steps to interpret the results. The first thing you should do is re-write the odds ratio in a simpler, more user-friendly form. If you were given an odds ratio of 6.7 comparing the risk of developing stomach ulcers in people who took antacids and aspirin vs those who took neither medication, you can change the odds ratio to ‘aspirin’ and ‘antacids’ to make it easier to compare to non-medicinal treatments like eating yogurt or drinking wine.

If you’re a person who regularly takes aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) to prevent heart attacks and strokes, you should know how important it is to continue these treatments even if you’ve been told that you have stomach ulcers. Because taking aspirin and NSAIDs reduces the risk of heart disease and other chronic conditions, these medications are known as ‘positive modifiers’ in the scientific community. If you’ve been tested for stomach ulcers and have been told that you have the disease, then it’s important to keep taking aspirin and NSAIDs to maintain its protective effects.

If you’re interested in comparing the likelihood of developing heart disease in people who smoke to those who don’t, you should look at the odds of developing heart disease in people who don’t smoke. If you see that the odds of getting the disease are 3 times higher in people who smoke, you can conclude that, for every 100 people who don’t smoke, 33 will develop heart disease. It’s important to keep in mind, though, that just because the odds are higher in one group doesn’t mean that the other is safe. For example, if you’re a female who doesn’t smoke and in your fifties, you have an odds ratio of 22.7 for heart disease, it doesn’t mean that, compared to a male in their fifties, you don’t have a greater chance of developing heart disease. It means that, compared to a male in their fifties, your odds of getting the disease are 22.7 times greater.

If you see that the odds of getting a particular disease are higher in one group than another, take into consideration a few things. First, is being in the higher-risk group a true risk for the disease? Second, is the disease common in the population being studied? And third, what was the study design and what does it mean for the general population?

## How Is The Odds Ratio Calculated?

To calculate the odds ratio for a specific study, you need to know a few things. First, which group is being compared to what group? Second, what is the occurrence rate of ‘X’ in the first group and ‘Y’ in the second group? Third, what is the size of each group?

If you’re comparing the risk of developing stomach ulcers in people taking antacids and aspirin to those taking neither medication, the first group would be people who take antacids and the second group would be people who take aspirin. If we assume that, as a general rule, antacids and aspirin don’t cause stomach ulcers, then the odds ratio would be calculated as follows:

(Number of people who took antacids and aspirin)/(Number of people who took neither medication) X (Number of people who developed stomach ulcers in people who took antacids and aspirin)/(Number of people who took neither medication) X (Number of people who took antacids and aspirin)/(Number of people who took neither medication)

(Number of people who took antacids and aspirin)/(Number of people who took neither medication) X (Number of people who developed stomach ulcers in people who took aspirin)/(Number of people who took neither medication) X (Number of people who took antacids and aspirin)/(Number of people who took neither medication)

(Number of people who took antacids and aspirin)/(Number of people who took neither medication) X (Number of people who developed stomach ulcers in people who took aspirin)/(Number of people who took neither medication) X (Number of people who took antacids and aspirin)/(Number of people who took neither medication)

Let’s do some examples. First, if you’re comparing the risk of getting stomach ulcers in people who smoke to those who don’t, the first group would be people who don’t smoke and the second group would be people who smoke. The odds ratio for this comparison is simply:

(Number of people who didn’t smoke)/(Number of people who smoked)

You don’t need to do any calculations to know that the odds of someone who doesn’t smoke developing stomach ulcers is 1 in 16 compared to someone who smokes. This is a simple example of how an odds ratio is usually calculated, but it’s important to keep in mind that there are many different ways to calculate it depending on the information provided by the study.

## What Is The ‘Oddest Ratio’?

Sometimes, instead of comparing the occurrence rate of two different diseases or conditions in two groups of people, scientists will compare the odds of just one disease or condition occurring in a group of people to another group. This is called the ‘odds ratio’ or ‘relative risk’ for the disease or condition being compared. This is done for various reasons, but if you’re curious, it means that you’re comparing the odds of just one event (e.g. heart disease) happening in a group of people to another group.

For example, if you’re interested in comparing the risk of heart disease in people who take aspirin with those who don’t, you can look at the odds of getting a heart attack or stroke in people who take aspirin. If you see that the odds of getting a heart attack or stroke are twice as high in people who take aspirin than those who don’t, you can conclude that, compared to those who don’t take aspirin, the odds of getting a heart attack or stroke are twice as high in people who take aspirin.