Final answer:
The real cause of the increase in output at Western Electric's Hawthorne plant was the Hawthorne effect, which is the increase in performance due to the awareness of being observed by researchers or supervisors.
Step-by-step explanation:
The real cause of the increase in output at Western Electric's Hawthorne plant was the Hawthorne effect. The Hawthorne effect refers to the increase in performance of individuals who are aware they are being observed by researchers or supervisors.
The original researchers found that any change in a variable, such as lighting levels, led to an improvement in productivity, even when the change was negative. This concept of the Hawthorne effect is still considered an important factor in experimental studies today.