Question

How to tell (know) if an explanatory variable has impact or not and how much?

Answer 1

To test the explanatory power of the whole set of explanatory variables, as compared to just using the overall mean of the outcome variable, use the F-statistic and the p-value printed by SPSS or Excel under “ANOVA.” If this p-value is less than 0.05, you can reject the null hypothesis (which is that all of the variables have coefficients of zero) at the 5% significance level. If the p-value is less than 0.01 you can reject at the 1% significance level.