In evaluating the performance of new hires, the human resources division found that candidates with higher scores on its qualifying exam performed better. In a multiple regression that also used the...

In evaluating the performance of new hires, the human resources division found that candidates with higher scores on its qualifying exam performed better. In a multiple regression that also used the education of the new hire as an explanatory variable, the slope for test score was near zero. Explain this paradox for the manager of the human resources division.