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Old 08 February 2014, 03:12 AM
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Hero_Mike Hero_Mike is offline
Join Date: 06 April 2005
Location: Phoenix, AZ & Hamilton, ON
Posts: 7,267

Originally Posted by ganzfeld View Post
I don't understand your computations. Especially this part.
*sigh* Microsoft Excel works very well for this.

Using the above rates (true positive 99.7%, true negative 99.95%), an infection rate of 0.6%, and a population of 1 million, here's what I get.

1,000,000 total

994,000 healthy and 6,000 infected

5,982 true positives and 18 false negatives

993,503 true negatives and 497 false positives

So 5,982 true positives out of 6,479 total positives or 92.329% chance that a positive is true.

The ratio of 92.329% over 0.6% is 154 - when the disease is very rare, this tends to an upper bound of the accuracy of the test, which in this case is 1:1990

Last edited by Hero_Mike; 08 February 2014 at 03:13 AM. Reason: All values rounded to zero decimal places per standard rules in Excel.
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