The personnel department of a large manufacturing firm selected a random sample of 23 workers. The workers were interviewed and given several tests. On the basis of the test results, the following variables were investigated: X2 = manual dexterity score, X3= mental aptitude score, and X4= personnel assessment score.

Subsequently, the workers were observed in order to determine the average number of units of work completed (Y) in a given time period for each worker. Regression analysis yielded these results:

y= 212 + 1.90X2 + 2.00X3 + 0.25X4

Which of the following statements is the correct interpretation of the mental aptitude regression coefficient?

Select one:

a.If we increase mental aptitude by one unit, holding the other predictor variables constant, units of work completed will decrease by an average of 0.6.

b.If we increase mental aptitude by one unit, holding the other predictor variables constant, units of work completed will increase by an average of 2.0.

c.If we increase units of work completed by one unit, holding the other predictor variables constant, the mental aptitude score will increase by an average of 2.0.

d.If we increase mental aptitude by one unit, holding the other predictor variables constant, units of work completed will increase by an average of 0.6.