The Hawthorne Effect is when an individual is being observed under an experimental study in order to improve or change their behaviour; in this experiment the individual only changes their behaviour because of the knowledge of being monitored. 

It can be challenging to carry out this experiment as it might not be as accurate as the employee is conscious about the fact that their behaviour is being monitored; therefore employers could perhaps ensure that when such an experiment is being carried out, the employee is not informed about it.