Your Textbook Reports the Following Result from an Two-Way Fixed

Essay

Your textbook reports the following result from an two-way fixed effects (entity and time fixed effects)regression model: = -0.66 BeerTax + StateFixedEffects + TimeFixedEffects
(0.36)
Where the number in parenthesis is the heteroskedasticity- and autocorrelation-consistent (HAC)standard error.
a.Calculate the t-statistic.Can you reject the null hypothesis that the slope coefficient is zero in the population,using a two-sided test and a 5% significance level?
b.Given that economic theory suggests that the population slope is negative under the alternative hypothesis,is it possible to use a one-sided test here? In that case,does your conclusion change?
c.Using only heteroskedasticity-robust standard errors,but not HAC standard errors,the value in parenthesis becomes 0.25.Repeat the calculations in (a)and report your decision based on a two-sided test.
d.Since the coefficient becomes more statistically significant in (d),should this influence your choice of standard errors? Why or why not?