19. Refer to Tables 11.5 and 11.7. Note that X1 and X2 lose their significance after entering the interaction term, even though that term is not significant

a) Explain why this happens

b) Rerun the interaction inodel, after centering the predictor scores about their mean. that is. take X = X, - 44.425 and take X = X2-56.60. Note that now the estimates and their standard errors resemble those for the no-interaction model. This is a useful way of dealing with multicollineanty for models that have interaction or quadiatic terms