sylvia hope sylvia.hope at CASMAIL.CALACADEMY.ORG
Sun Dec 7 20:07:27 CST 1997

          This is in re all the discussion of "corroboration" - just
          want to suggest that bootstrapping is not corroboration and
          is misleading as a measure of confidence in a phylogeny.

          In psychological parlance, the distinction between
          reliability and validity is clear (or used to be back when I
          studied psych).  Reliability is how repeatable an outcome
          is, given the same data set.  Validity is how well a data
          set corresponds to some outside criterion (corroboration).
          For example "split-half" reliability correlates scores on
          half of test items with scores on the other half.  The
          extent of correlation indicates how well individual items
          are measuring the *same thing*, NOT how well they are
          measuring any *particular* thing.  No one trained in psych.
          testing mistakes reliability for validity.

          Bootstrapping is a test of internal consistency of a data
          set and therefore a test of *reliability*, not *validity.*

Sylvia Hope
Dept. of Ornithology and Mammalogy    *
California Academy of Sciences        *
Golden Gate Park                      *
San Francisco, CA, USA 94118          *
email:  sylvia.hope at    *
phone:  (415) 750-7176                *
fax:    (415) 750-7137                *

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