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?