Testing Homoskedasticity in Cross-sectional Spatial Autoregressive Models

Abstract

In this paper, we suggest an outer-product-of-gradient (OPG) variant of Lagrange multiplier (LM) test statistic for testing homoskedasticity in cross-sectional spatial autoregressive models. We use the OPG method to estimate the asymptotic variance of the score functions in a quasi-maximum likelihood (QML) setting. We use the OPG variance estimate to develop a robust test statistic in the local presence of spatial parameters. Under some general assumptions, we establish the asymptotic distribution of our test statistic under the null and local alternative hypotheses. In a Monte Carlo simulation, we investigate the finite sample size and power properties of our test. Our simulation results show that our tests work well in finite samples.