Assume that a researcher is interested in variables that might affect infant birth weight. The researcher performs a stepwise multiple regression to predict birth weight and includes the following independent variables: (1) number of cigarettes the mother smokes per day, (2) number of alcoholic drinks the mother has per day, (3) weight of the mother. If the statistical program produces a regression that includes only the first two independent variables, what can we conclude about the third variable, weight of mother?