The deviance is an important statistic as it enables the contribution made by explanatory variables to the prediction of the response variable to be determined. If by adding a variable to the model, the deviance is greatly reduced, the added variable con be said to have dad a large effect on the prediction of Y for that model. If, on the other hand, the deviance is not greatly reduced, the added variable can be said to have had effect on the prediction of Y for that model. The change in the deviance that results from the explanatory variable being added to the model is use to determine the significance of that variable’s effect on the prediction of Y that model. To assess the effect that a single explanatory variable has on the prediction of Y, one simply compares the deviance statistics before and after the variable has been added to the model. For a simple OLS regression model, the effect of the explanatory variable can be assessed by comparing the RSS statistic for the full regression model (Y=a+ βx) with that for the null model (Y=a). The difference in deviance between the nested models con then be tested for significance using an F-test computed from the following equation.