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Re: Govt has right to block testing for mad cow disease, court rules
From: David Farber <dave () farber net>
Date: Mon, 1 Sep 2008 07:52:18 -0400

Begin forwarded message:

From: Valdis.Kletnieks () vt edu
Date: September 1, 2008 4:02:03 AM EDT
To: dave () farber net
Cc: ip <ip () v2 listbox com>
Subject: Re: [IP] Re: Govt has right to block testing for mad cow disease, court rules

On Sun, 30 Aug 2008 8:28:48 PM EDT, Dave Wilson said:

Basically a federal appeals court has ruled that the government, which
controls test kits for mad cow disease, has the authority to prevent a
single beef exporter from testing 100 per cent of their livestock for
the disease.  The US Department of Agriculture (USDA) argues that
because there is typically a minimum two year incubation period for
the disease, and US cows are typically slaughtered before the age of
two, 100 per cent testing would give consumers a "false sense of

The USDA is in fact correct there. The company could test 100% of its cattle, which were 100% contaminated with mad cow, and pass every single head because the test wouldn't detect it at the stage the cattle are usually slaughtered. As a result, the testing *would* create a false sense of security. There's also issues with the well-understood "base rate fallacy" - if you're testing for an fairly rare event with a test that has a noticable false- positive rate, you drown in false positives (for instance, if 1 in 100,000 cattle actually have mad cow, but the test has a 1% false positive rate, then testing all
the cattle will have 1 actual positive, and 1,000 false positives).

One has to however wonder why the USDA then turns around and uses *that
same exact test in the same incorrect manner* to test 1% of the cattle...

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