| We decided on four lags as a reasonable choice, because error autocorrelation and heteroscedasticity problems disappear in these circumstances. |
| Standard errors are in parentheses, and are corrected for heteroscedasticity using the procedure developed by White. |
| We used modified Wald-statistic for assessing heteroscedasticity of group variance among remains of the fixed-effects regression model. |
| All expenditures are analyzed using Ordinary Least Squares regressions weighted to reflect the population and to correct for heteroscedasticity. |
| Absolute values of t-statistics are adjusted for heteroscedasticity of errors at a firm level. |
| The generalized autoregressive heteroscedasticity technique improved the explanatory power of the model. |
