[Clips] Read two biometrics, get worse results - how it works

[mheyman at gmail.com]

On 10/19/05, R.A. Hettinga <rah at shipwright.com> wrote:
>
>  [EDIT]
>  Daugman presents
>  (http://www.cl.cam.ac.uk/users/jgd1000/combine/combine.html) the two rival
>  intuitions, then does the maths. On the one hand, a combination of
>  different tests should improve performance, because more information is
>  better than less information. But on the other, the combination of a strong
>  test with a weak test to an extent averages the result, so the result
>  should be less reliable than if one were relying solely on the strong test.
>
I believe the Daugman results are correct only when one accepts
results where the tests disagree. That is, if the first test returns
positive and the second test returns negative, you chose the overall
results to be positive or negative as opposed to "do over until they
agree".

Of course, in real life with knowledge of the physics of the tests and
the ability to pull out non-boolean results, one may be able to remove
many of the "do over" results to keep from annoying the test subjects.

-Michael Heyman

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