GynoGab Math: Can't Skip this Lesson

When you go to the gyno to get tested...for anything....the test may be a positive test or a negative test, and actually the test might be inconclusive, but lets not deal with those today. Mathematics enters the scene from the beginning, and then again after you get your results. Most of us think the math of any one test is "the percent chance that my test, if I get it, will be normal" or the "percent chance that it will be abnormal" and, yes, that is the way math first enters your discussion. Depending on that math, you may or may not want to take the test, or you may o may not want to spend your money on the test. But it gets more mathematically complex from here. What you want to know, is if you had a positive test what was the percent chance this positive was correct...and what is the chance that it was not correct? And so to, with a negative test, if you are told that it is negative, what percent chance do you have of actually getting a negative test but having it be positive?  So if you had a test that was positive and you don't have the disease it is called a false positive, and if you have a negative, but you do have the disease, it is called a false negative. The statistical chance that the test was right when it said positive is it's positive predictive value to the mathematicians. If you had a negative test and it was correct, you do not have the condition, it is the test's negative predictive value. The math can get complex quickly because it is different for each test we use medically. It also gets many times more complex if you consider that you have the test more than once. Your chances of  getting it wrong on multiple occasions is much less. This math is dependent on the test itself, but it also is dependent on you, those likely to have a condition, are less likely (statistically) to have their test be accurate. If we consider everyone with the disease (if we knew that for sure) and we compare this to everyone with a positive test we find out how sensitive the test is. So a test that is 100% accurate would be the most sensitive test there is, we don't have any of those in medicine! We say a test is very specific if in fact all the people without the disease get a negative test result, it is much less specific if people with the disease are told to be negative. Now when you get your medical test results, you should be reviewing this math with your gyno. a tiny bit We know this as a basic concept, and often, especially with some very crucial tests, like mammograms, we do discuss this issue. Most of us gynos are guilty when we tell you a test result and fail to give the "fair warning" of the math of the discussion. Just remember, at the end of the day, one test, is just one test, and it takes more than that to make an accurate diagnosis. If you want to know more about a particular screening test, go to this on line journal. And it's important to discuss that concept with your gyno, for all your tests!


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