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 `In medical statstistics, what are natural frequencies and absolute risks?`
 ```I have posted an answer to your question below. Please let me know if you have further questions or if I can clarify this for you, especially if you have questions related to a specific procedure. 1. Natural frequencies A frequency is a measurement of how often something happens. It can be thought of as similar to a rate. For example, if there are 100,000 people living in a town and each year 20 get the chicken pox, the frequency is 200 per 100,000 per year. A natural frequency is the frequency of some event or disease in the general population. For example, the example above is a natural frequency of chicken pox, with no vaccine. If a vaccine were given, the actual frequency of chicken pox would go down (less people would get it) maybe to 10 per 100,000 per year and be less than the natural frequency. In other words, an intervention of some kind may change the frequency to be something other than the natural frequency. You can imagine a town with radioactive waste will have a frequency of cancer that is higher than the natural frequency, and a country that uses 2. Absolute risks There are different kinds of risks in medical statistics (epidemiology). An absolute risk is the true probability of some event affecting someone in a particular population. For example, the risk of a heavy smoker getting lung cancer might be 10%. This is different than a relative risk. A relative risk is a comparison between two risks. For example, if a non-smoker has a 1% chance of getting cancer, the heavy smoker's relative risk is 100. As you can see, if we look at relative risks we may get very different numbers compared to absolute risks. Sometimes researchers or companies will report relative risks (or a difference between risks, called a risk reduction) because they sound more dramatic. For example, they will say that a using a certain medication will reduce your risk of heart attack by 50%. This sounds amazing, but if the risk of heart attack WITHOUT taking the medicine is very small (the absolute risk is very small), then a 50% reduction is not very much. It might only be a change from 1/2% to 1/4% or less. In general, it is more accurate to look at absolute risks when deciding on a procedure or a treatment, because it tells you the true probability of something happening. I hope this helps, RMH Absolute and relative risk http://info.cancerresearchuk.org/cancerandresearch/risk/communicatingrisk/absoluteandrelativerisk/ Weighing treatment pros and cons http://www.breastcancer.org/treatment_stats.html```