If so, the news is not necessarily good for proponents of winner-take-all systems. The direction of Bolivian electoral reform was from more to less proportionality - in particular, the addition of single-member districts.

A new study by Miguel Centellas finds evidence that Bolivia’s move from regional list PR to a mixed member system has destabilized the country’s party system. Destabilization has manifested most significantly in Andean voters’ migration to anti-system parties.

Why? One explanation is that the use of plurality SMD districts tended to tie parties closer to specific constituent, rather than national, interests. In a multiparty system, most SMD legislators were elected by small pluralities, not majorities. This seems to have encouraged parties to target their electoral message to a narrow base in order to better win SMD seats. The evidence also suggests that Bolivian politics (prior to 2002) had a centripetal tendency, pulling parties closer to the political center. In contrast, politics since 2002 has tended towards powerful centrifugal tendencies and a high degree of polarization (particularly regional polarization). Such a shift has negative consequences for political stability, as well as for future democratic prospects.

If this is the case, could implementing a majority requirement (and some form of runoff) in the nominal tier dampen the centrifugal tendency of the new system? Or would single-member districts trump?