The Public Policy Institute of California looked at the impact
of two reforms.
First, the new legislative and congressional districts drawn
by an independent citizens' commission.
And second, the "top-two" primary system. That allows voters
to cast ballots for any candidate regardless of party, but only the
top two candidates advance.
The PPIC study found that every incumbent advanced to the fall
election as did virtually every new candidate endorsed by a major
Redistricting helped increase the number of competitive seats
between the two major parties...but the tendency of Republicans and
Democrats to live in different parts of California prevented bigger
The top-two primary also resulted in the near elimination of
minor party candidates in the fall election.
The study suggests that the reforms were pretty much in line
with what would have been expected under the old system.