Rein Taagepera,
"Implications of the Effective Number of Parties for Cabinet
Formation," Party Politics, 8 (March, 2002),
227236.
First Paragraph:
How does the number of parties in a representative assembly
affect the type of cabinets formed? The question is
important because cabinet durations and working styles tend
to differ depending on whether one has, say, a multiparty
minority cabinet or a oneparty majority cabinet  and the
latter looks more likely when the assembly includes few
parties. The issue can be investigated on various levels,
depending on the specificity of information taken into
account. When the seat shares of all parties are known, a
game theoretical analysis for this particular constellation
is possible, the more so when the parties' ideological
stands are also available. But taking into account only a
single major indicator, the effective number of parties,1
can yield important generalizations across many countries.
This is the approach taken here, to explain how cabinet
level concentration of power is constrained by party level
concentration of seats.
Figures and Tables:
Table 1. Average frequencies (%) of five cabinet types at
various effective numbers of parties
Figure 1. Cumulative percent frequencies of cabinet types
versus effective number of legislative parties.
Figure 2. Minimum number of partners (p) needed to form a
minimalwinning coalition, depending on the effective number
(N) of legislative parties: theoretical limits and averages
of actual elections (from Table 2)
Table 2. Minimum number of partners (p) needed to form a
minimalwinning coalition, depending on the effective number
(N) of legislative parties in actual elections
Last Paragraph:
Lijphart's (1999: 110) measure of 'MW cabinets and oneparty
cabinets' (MW/OP) may look confusing and artificial but can
be reworded  and one is hard put to find a more suitable
single index to express the distribution of cabinet types.
Its strong correlation with the effective number of
legislative parties is not an empirical happenstance, but is
logically imposed to an appreciable degree. In this sense,
the effective number of parties is the independent variable
driving MW/OP. In turn, going in the opposite direction,
MW/OP supplies a way to visualize the meaning of the
effective number for constellations where the image of
equivalence to some number of equalsized parties becomes
stretched. This conceptually reinforced logical tie between
the two core indices to measure the degree of
majoritarianism/ consensualism of a country adds credibility
to both of them.
