Estimating the Nonlinear Demand for Defense Burden and its Income Elasticity in Iran According to the Level of International Threats

This paper investigates the nonlinear demand for defense burden function and its income elasticity in Iran for the period of 1991 to 2015 using Smooth Transition Regression (STR) model. For this end, the Average defense burden in Middle Eastern countries is used as the international threats indicator (inverse security index) and transition variable. Moreover, considering one transition function with one threshold parameter, that represents a two-regime model, is sufficient to specification of nonlinear relationship among variables. The results indicate that the threshold value is 8.28 percent and the estimated slope parameter is 1.88. In the first regime, the income elasticity of defense burden is negative and with a one percent increase in income, the defense burden is reduced by about 0.05%. In the second regime, the income elasticity of defense burden is positive and with a one percent increase in income, the defense burden increases by about 0.03%. Therefore, there is a U-inverse relationship between income and defense burden in Iran, according to the level of security. According to other results, the coefficients of the impact of non-defense expenditure, population, international threats and oil revenues in the first limiting regimen are negative, meaningless, positive and positive. But in the second limiting regime where the level of international threats is higher than the threshold, the severity of this effect (without changing the sign) increases.