Consider a disease whose prevalence is one in a thousand. A test to detect the disease has a false positive rate of 5 percent. What is the chance that a person found to have a positive test result actually has the disease?

Assume that 1000 individuals are administered the test. Of these people, only 1 person has the disease, per the above. Of the other 999 people without the disease, 50 (mathematically the number is 49.95 = 50/999) will still test positive because of the test’s false positive of 5%. Therefore, 51 (mathematically the number is 50.95) people will test positive in a group of 1000 people. But only 1 person in those 51 people actually has the disease. Therefore, the chance that a person found to have a positive test result actually having the diseaese is 1/51 = 0.0196, or about 2%

With mammograms, false positive rates can be around 15%, depending on the radiologist.

It is publicized that the chances of a woman developing Breast Cancer in her lifetime in the US is presently about 1 out of 8. That's 125 / 1000.

***** Let's assume a woman begins getting annual mammograms at age 30, and continues until she's about 72. That's 42 years. 125 divided by 42 is about 3. This means that 3/1000 women who show up for a given mammogram, on average, will actually have breast cancer. ****** THOSE ARE YOUR ACTUAL CHANCES, JUST 3/1000.

Based on the 1/8 Breast Cancer rates in the US and 42 annual mammograms beginning at age 30, of 1000 women are administered a mammogram at their annual checkup, only 3 will actually have the disease. Of the other 997 women without the disease, 150 (mathematically the number is 149.55) will still test positive based on a test’s false positive rate of 15%. Therefore, 153 women will test positive in a group of 1000 people. But only 3 women in those 153 women actually have the disease. Therefore, the chance that a woman found to have a positive mammogram test result actually having the diseaese is about 3/153 = 0.0196. So, if you get a positive mammogram, it means there is only a 2% chance that you really have breast cancer.

Stated another way: A POSITIVE MAMMOGRAM TEST MEANS THERE IS A ABOUT 98% CHANCE THAT YOU DON'T HAVE Breast Cancer (depending on the skill of the radiologist).

Why take such a test with such poor results ????? Because your doctor and the media tell you to ????

You can try the above with different numbers for the false positive rate, but what you typically find is that mammography is essentially worthless, other than as a cash-generator and scare tactic, when compared to other methods such as thermography. If you get a positive result, there is always at least about a 90% chance that the mammogram is wrong.

Personally, I conclude that mammograms are a humiliating waste of time and money, and most women only have them performed out of FEAR.