In attempting to estimate the causal effect of employee hours worked on total units produced, you include the age of the production equipment as a control variable. Which of the following conditions would not be a good reason to include this control variable?
A) Older production equipment often requires more employees to work on them.
B) Older production equipment often is less productive (i.e., produce fewer units on average).
C) The age distribution of the plants is highly non-normal.
D) The semi-partial correlation of total units produced on age of the machine holding number of employees fixed is positive and statistically significant.

Question

Quizplus · Accepted Answer

The age distribution of the plants being non-normal would not be a good reason to include age of the production equipment as a control variable. Non-normality would not affect the relationship between employee hours worked and total units produced nor would it affect the relationship between age of the equipment and total units produced. It would only affect the distribution of the age variable itself. A, B, and D are all good reasons to include age of the production equipment as a control variable because they suggest that age of the equipment may be associated with total units produced and could potentially confound the relationship between employee hours worked and total units produced.

In Attempting to Estimate the Causal Effect of Employee Hours