Chapter 6 Why Authoritarian Parties? The Regime Party as an ...

CHAPTER 6
Table 6.5: Three subgroups of authoritarian regime parties by legislative seat share
Subgroup Fraction Legislative Seat Share
Mean Variance 95% Conf. Int.
Dominant/hegemonic parties 69.35% 75.78 11.93 (73.41,78.15)
Parties under competitive auth. 22.88% 51.39 7.04 (48.90,53.88)
Transitional cases 7.78% 19.57 7.55 (17.21,21.94)
Note: The unit of observation is a country-year. Maximum-likelihood estimates of a 3-component mixture
of Normal densities.
by authoritarian regime parties across all dictatorships with multiple parties.
A notable feature of the distribution in Figure 6.2 is that it appears to contain three
qualitatively distinct groups of observations. Going from left to right, there first appears to
be small subset of regime parties that only have a minority of legislative seats, next there
is a larger group of parties that on average control a bare majority of legislative seats, and
finally, there is a large group of regime parties that command a supermajority of legislative
seats.
In order to better understand and quantify the differences between these three groups,
I fit to this data a mixture of three Normal densities. 31 As Table 6.5 summarizes and the
density plots in Figure 6.2 illustrate, the three groups are reasonably well represented by
Normal densities with mean seat shares of 19.57, 51.39, and 75.78. The estimates in Table
6.5 also indicate that the three groups are distinct: the 95% confidence intervals for the three
means do not overlap.
The largest of these subgroups contains roughly 69% of all observations and describes
31 Since the share of legislative seats is bounded between 0 and 1, the Normal distribution is not the
most appropriate probability model for this setting; I adopt it primarily because its parameters are easily
interpreted. On the estimation of finite mixture models, see McLachlan and Peel (2000).
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