We also include a number of variables that previous studies have linked to the formation
of PTAs to ensure that any observed effect of veto points is not due to other international or
domestic factors. Past research has found that democracies tend to join PTAs at a higher rate
than non-democracies (Mansfield, Milner, and Rosendorff 2002). Consequently, we introduce
Regime Type
i
and Regime Type
j
, which are 21-point indices of country i’s and country j’s regime
type in year t. These variables are constructed using the Polity data set. They range from 10 for
the most democratic states to –10 for the most autocratic ones (Jaggers and Gurr 1995). As such,
we expect them to be directly related to the onset of PTAs.
variable since it captures some of the same institutional features as Veto Points
i
and Veto Points
j
(for example, constitutionally mandated limitations on executive authority). We need to ensure
that the influence of veto players is not simply an outgrowth of the effects of regime type.
Next,
Trade
ij
is the logarithm of the total value of trade (in constant 1995 US dollars)
between countries i and j in year t. Various observers argue that increasing economic exchange
creates incentives for domestic groups that benefit as a result to press governments to enter
PTAs, since these arrangements help to avert the possibility that trade relations will break down
in the future (Nye 1988). Moreover, heightened overseas commerce can increase the
susceptibility of firms to predatory behavior by foreign governments, prompting firms to press
fewer countries than Henisz’s measure and it only covers the period from 1975 onward. Using the Beck et al.
measure rather than Henisz’s measure cuts the size of our sample in half, which is clearly undesirable. However,
there is a good deal of agreement between Henisz’s measure and Beck at al.’s measure where those samples overlap
– the correlation between a country’s annual score on Henisz’s measure of veto players and its score on the Beck et
al. measure is about .75, suggesting that our results are not driven by the choice of measure.
15
We use Gleditsch's (2004) update of the Polity IV data set (Marshall 2004), which includes data on smaller states
excluded by the Polity project, but included in the Correlates of War Project list of system members.
18
Convention