Probabilities (General)

by David Turell , Friday, April 18, 2014, 02:50 (3871 days ago) @ romansh


> Romansh: The piece of information missing is the incidence of the ailment in the relevant population. 
> 
> If the good doctor would go on and explain that the incidence of the ailment in "my" population was say one in a thousand then we can calculate what my chances of suffering from said ailment.
> 
> Say we took a thousand people (representative of the population) we would expect, on average, one real positive and fifty false postives. 
> 
> So my actual chances of suffering from said ailment are about one in fifty or two percent and not the ninety five percent I had originally calculated. Obviously the numbers will vary with the type of ailment and test.-But your comment does not fit my experience. As a practicing physician I might see one of 'these' and one of 'those' rarities in a lifetime. I would have no statistics within my city's patient population available to me to have any way to get to your requirement. I understand your added step adds to the confidence limits of the statistical judgment, but I'm not even sure the Houston health department could help me. On the other hand, in epidemiological studies that type of informaton is invaluable. In my first book I have a section on the political misuse of statistics.