1
Party switching has been a common phenomenon on in the early years of the
Ukrainian Verkhovna Rada. Between March 1998 and July 2003, 937 deputies served in
the Rada. Combined, these deputies switched parties 477 times during 12 legislative
sessions.
1
Given the stability of party affiliation in older, established legislatures like the
US Congress, what could explain this behavior?
2
One place to begin looking for an
answer to this question is the burgeoning literature on in other legislatures (e.g.,
Desposato 1997, forthcoming; Heller and Mershon 2003, 2005; Laver and Bennoit 2003;
Mann 2000; McElroy 2003; Meija-Acosta 1999; Nokken and Poole 2004). While there
are certainly differences between contexts, this extant literature points to the interplay
between electoral incentives, policy demands, and institutions, in particular electoral
systems, as sources for party switching.
While the existing literature creates a solid foundation for understanding the
motivations of party switching, the existing methods used to model party switching
remain problematic. Typically, scholars have used two methods model party switching:
logit or probit estimations on a dichotomous dependent variable indicating a legislator
left his or her party (models of party defection) and conditional fixed-effects logit
estimations on a dependent variable that indicates which party a legislator chooses in a
given time period (models of party selection).
3
While the results from such models are
useful, they have significant limitations. Models of defection may tell us why a legislator
might leave a party; however, the models contain no information about potential
alternative parties. Thus, the models are inaccurate if we assume, and I think safely
1
All deputies whose party affiliation at the end of the legislative session was different from their party
affiliation at the beginning of the session are coded as having switched parties.
2
Nokken and Poole (2004) find only 160 party switchers in the US Congress over a 163 year period.
3
In the literature on party switching, such models are also referred to mixed logit models (McElroy).
Convention