The occurrence of false positives [in some experiment] is 40%What does this mean? Does it mean that 40% of positives are false? Or 40% of all tested patients are specifically both false and positive? Or say 40% of those that are false are positive?

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notemilyu1208 · Accepted Answer

It means (mostly in medical testing) that the binary outcome of the model is falsely indicated as positive. Meaning that the test says that the condition is present, while in reality, it is not.This is important in statistical hypothesis testing and especially in medical testing, because it can create some false interpretation of the accuracy of a test. Let me clarify with an example:I recently read an article in a Belgian newspaper that said that a test was   99  % accuracy, but if you tested positive, you only had   1  % chance that you actually had the disease. The ratio of people that had this disease was      1    10000  and claimed to be   99  % accurate. So let&#039;s assume you have   1.000.000 people,   100 people should have the disease. But if you were out to test it,   99 of these   100 would get a true positive and   1 of these   100 people would get a false negative. On the other hand, of the   999.900 people who don&#039;t have the disease,   989.901 people would get a true negative and   9999 people would get a false positive. This means that the probability you actually would have the disease if you were to test positive is only       99    10098    ≈  0.98  %  .  .

tuehanhyd8ml · Accepted Answer

Let   D indicate the presence of a disease. Let   + indicate that the experiment shows a positive and a − shows a negative. Thus,(  +  ∣  D) indicates that the person has the disease, and the experiment showed a positive result, i.e a true positive.(  −  ∣  D) indicates that the person has the disease, and the experiment showed a negative result, i.e a false negative.(  +  ∣      D    c  ) indicates that the person does not have the disease, and the experiment showed a positive, i.e a false positive, which has the 40% chance.(  −  ∣      D    c  ) indicates that the person does not have the disease, and the experiment showed a negative, i.e a true negative.Thus, the statement &quot;The occurrence of false positives [in some experiment] is   40  %&quot; indicates that a   40  % of people that are not sick with the disease will show a positive in the test. In other words   P  r  (  +  ∣      D    c    )  =  0.4  =  40  %

The occurrence of false positives [in some experiment] is 40% What

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