agreement & frequency

[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.

Andrew
--

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