I'm confused, and surely wrong, about the cancer example.
1 in 10000 people are sick. 1 sick person : 9999 well persons
multiply by 100: 100 sick people : 999900 well persons
99% of the sick people have positive tests: (0.99 * 100 = ) 99 Positive tests
1% of the well people have false positive tests: (0.01 * 999900 = 9999)
Using the odds view: number of sick persons with positive tests / total number of persons with positive tests: (99 / (99 + 9999) = 99 / 10098. Multiply top and bottom by (1/99) => (99/99) / (10098/99) = 1 / 102. The text says the ... (read more)
I'm confused, and surely wrong, about the cancer example.
1 in 10000 people are sick. 1 sick person : 9999 well persons multiply by 100: 100 sick people : 999900 well persons 99% of the sick people have positive tests: (0.99 * 100 = ) 99 Positive tests 1% of the well people have false positive tests: (0.01 * 999900 = 9999)
Using the odds view: number of sick persons with positive tests / total number of persons with positive tests: (99 / (99 + 9999) = 99 / 10098. Multiply top and bottom by (1/99) => (99/99) / (10098/99) = 1 / 102. The text says the ... (read more)