A number of necessary control variables are also included. Wealth refers to the
logged value of gross domestic product per capita (GDP), held constant in 1996
dollars (Gleditsch 2002). Growth measures the year-to-year change in real per capita
GDP. A benefit of dyadic analysis is the ability to control for important factors such
as alliances, joint democracy, power ratio, peace years, and distance. Allies are
coded with the Alliance and Treaty Obligations (ATOP) data set and is coded 1 if
the dyad members are considered to be in a ‘‘formal agreement . . . to cooperate
militarily in the face of a potential or realized military conflict’’ (Leeds 2005, 4).
Joint democracy is a dichotomous variable coded 1 if both members of the dyad
score above þ5 on the Polity IV scale. I also incorporate dummy variables for
whether the initiator (Dem. Initiator) or target (Dem. Target) is a democracy. Power
ratio relies on Correlates of War’s (COW’s) Composite Index of National
Capabilities (CINC). A state’s CINC score is constructed by aggregating the number
of military personnel, military expenditures, iron and steel production, energy consumption,
and total and urban population. For power ratio, I divide the initiator’s
capabilities by the total capabilities of the dyad. A value of 1 would indicate the
initiator has a complete preponderance of power over the other dyad member. A
state is believed to be more likely to initiate a dispute as the power ratio increases.
Peace years records the years since a conflict was last initiated in the dyad. I also
incorporate squared and cubic polynomials for peace years at the suggestion of
Carter and Signorino (2010). Finally, I use the natural log of the distance between
capitals to address geographical constraints on conflict. As two states are farther
from one another, they should be less likely to wage conflict.