Re: st: Comparing overlapping groups

[David Hoaglin <dchoaglin@gmail.com>]

Fred,

You're welcome.

If the people who have FM according to all four of the definitions
(FM1, FM2, FM3, and FM4) are the largest subset, you may want to make
that the "reference category" and use the coefficients for the
indicators of the other subsets to measure the effect of departures
from that main category.

One might hope that the four definitions agree for most people.
Otherwise, diagnosis of FM would seem chaotic.  The relative
frequencies of the 15 subsets may be of interest in themselves.

If the definitions are based on lists of symptoms or results of tests,
it may be instructive to use the individual symptoms or tests in the
analysis, instead of bundling them together as definitions.  This
approach may require some care if, for example, two definitions use
the same test but with different thresholds.

I haven't seen a question like yours in the literature, but that's not
saying much.  Perhaps someone else who reads this list can contribute
a reference or a link.

David Hoaglin
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