Question

click to correct the pronoun if needed. the hawthorne effect is the positive effect that a researcher or supervisor can have on employees performance at work merely by observing they and their productivity.

Explanation:

The pronoun "they" is incorrect as it is in the subjective - case and is the object of the verb "observing". It should be in the objective - case.

Answer:

The Hawthorne effect is the positive effect that a researcher or supervisor can have on employees' performance at work merely by observing them and their productivity.