frequency and agreement

[Andrew J. Koontz-Garboden]

Is anyone aware of work that has been done on grammatical agreement and
frequency?  For example, if a verb agrees with an object (variably) by
(variably)adding some sort of verbal inflection, at what point is there
generally considered to be "agreement."  Is it at 50%, 75%, 100% of the
time?

The particular phenomenon that I am working with is indirect object
clitic-doubling in Spanish.  This has been called agreement by many
working in formalist and functionalist frameworks.  I am interested in
at what point clitic-doubling ceases to be doubling and begins to be
grammatical agreement.  Any references to relevant literature (perhaps
in the field of grammaticalization?) would be greatly appreciated.  If
there is sufficent interest, I'll post a summary.

Andrew
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Andrew J. Koontz-Garboden
Department of Linguistics and
Department of Spanish and Portuguese
Indiana University
Ballantine Hall 848
Bloomington, IN 47405
U.S.A.