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Now, the same algorithm works if your test says negative.
We'll practice this in just 1 second. Suppose your test result says negative.
You could still ask the same question:
Now, what's my probability having cancer or not? But now all the positives in here become negatives.
The sum is the total probability of negative test results, and we may now divide by this score,
you now get the posterior probability for cancer and non-cancer assuming you had a
negative test result, which of course to be much, much more favorable
for you because none of us wants to have cancer.
So, look at this for a while and let's now do the calculation for the negative case
using the same numbers I gave you before,
and with the step by step this time around so it can really guide you through the process.