Basically, odds ratios are just the odds of an event occurring given exposure to a particular condition versus no exposure to the condition. For example, the odds of an infection occurring after surgery if there was a particular complication during the surgery versus no complication during surgery. Assuming that we will come across odds ratios commonly in published papers that we read, and are not going to be required to statistically derive these odds ourselves, we will go straight to interpreting odds ratios.
As in my previous blogs , I will try and keep this simple and use an example throughout for better understanding. An easy way to understand this is that an Odds ratio of 1 means that there are no odds of having the event of interest i. In other words, an odds ratio of 1 means that there are no higher or lower odds of the outcome happening. An odds ratio of above 1 means that there is a greater likelihood of having the outcome and an Odds ratio of below 1 means that there is a lesser likelihood of having the outcome.
Simple enough up to now? That means that if odds ratio is 1. If odds ratio is 1. You get the drift. Here the odds ratio would be 1. If odds ratio is 2. Here the odds ratio would be 3. For e. Here the odds ratio would be 0.
The odds ratio also shows the strength of the association between the variable and the outcome. Simply put, an odds ratio of 5 i. Lastly, the odds ratio tells us the direction of the association between the factor and the outcome. For example, an odds ratio of greater than 1 shows us a positive association between the outcome e. The direction of association may come intuitively to you but statistical backing makes a difference and shows that your data is robust enough.
Learning point: In a two by two table, for ease of calculation ensure that the outcome of interest is always at the top and the exposure on the left. According to the tablet above, individuals with endometrial cancer are 4. Master Critical Analysis by completing the Psych Scene online critical analysis course.
The Hub is a platform to share ideas, cases and concepts that bridge the gap between academia and the real world. Life in the Fast Lane ultra-concise summary. The odds ratio by Bland and Altman, of Bland-Altman plot fame. Wikipedia aka source of all statistical knowledge. How odds are used in gambling. Explaining odds ratios. More Top Articles. By Category. By Date. All Articles. Probability or Odds Probability Probability means the risk of an event happening divided by the total number of people at risk of having that event.
Risk Ratio RR is a very intuitive concept. So, the OR is 0. Pretend a new vape, Vapalicious, is associated with cancer. Why Does This Matter? What Does the OR Mean? So, what does an OR mean? In this study, Friese et al. Note: This table should have been changed because an OR value of 0. All that can be said is that the women who had an initial needle biopsy had fewer surgeries than women who did not have the biopsy.
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. Patients may decide to accept or forego painful or expensive treatments if they understand what their odds are for obtaining a desired result from the treatment.
Many patients want to be involved in decisions about their treatment, but to be able to participate effectively, they must have information about their likely results in terms they can understand.
At least in the industrialized world, most patients have received enough schooling to understand basic percentages and the meaning of probabilities. The odds ratio provides information that both clinicians and their patients can use for decision-making.
Odds ratios are one of a category of statistics clinicians often use to make treatment decisions. Other statistics commonly used to make treatment decisions include risk assessment statistics such as absolute risk reduction and relative risk reduction statistics.
The odds ratio supports clinical decisions by providing information on the odds of a particular outcome relative to the odds of another outcome. In the endocarditis example, the risk or odds of dying if treated with the new drug is relative to the risk odds of dying if treated with the standard treatment antibiotic protocol. Relative risk assessment statistics are particularly suited to diagnostic and treatment decision-making and will be addressed in a future paper.
Notes Potential conflict of interest. References 1. Prevalence and factors associated with aflatoxin contamination of peanuts from Western Kenya. International Journal of Food Microbiology ; Stampfer MJ. Veterinary Research ; Etter JF. Dependence on the nicotine gum in former smokers.
Addictive Behaviors ; Effect of treatment and adherence on ethnic differences in blood pressure control among adults with hypertension. Annals of Epidemiology ; Mylonakis E, Calderwood,SB. Infective endocarditis in adults.
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