

Quiz HN: Test your biases - jibiki

You are the minister of health.  Currently, you screen all citizens for cow-flu using test X.  You want to add another test, though, and you have two options: test Y or test Z.  Test Y is strongly correlated with test X.  Test Z is not correlated with test X.<p>Do you add test Y or test Z?
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tokenadult
Please provide more information. What is the specificity of each test? What is
the sensitivity of each test? And how virulent is the disease? And how
expensive is each test?

<http://en.wikipedia.org/wiki/Sensitivity_and_specificity>

<http://www.nhhealthcost.org/costByProcedure.aspx>

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jibiki
That's pretty much the right answer.

Let's say all tests cost the same and are 99% specific. Test X is at least 70%
sensitive. Test Y and Z have unknown sensitivity.

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yummyfajitas
All good tests should be strongly correlated with the presence/absence of
swine flue, and hence correlated with each other. So either tests X/Y are
broken, or test Z is broken. Or both.

We need to figure out which before answering the question.

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jibiki
Let's say X and Y are both good tests. Is it still possible you would prefer Z
to Y?

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cjg
If Z caught most of the cases that X missed, but not many that X caught then
it would be very useful.

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philwelch
My first instinct is to add test Z. Since Y correlates well with X, Z would
provide more information.

But if Y is correlated to X, that might indicate something about its
sensitivity.

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sharpn
If there are tests for a binary result (has cow-flu/does not have cow-flu)
that are not correlated, one or both of the tests is bad. Further information
could confirm or negate the choice of Y or Z (or sticking only with X).

