Reference #154: Peopleware
Employee turnover costs about 20% of all people-hour expenses. This is due to the cost involved in hiring a new employee, as well as the several months it takes for the employee to be fully productive.
During the early parts of this time, the employee is negatively productive as they rely on someone else to bring them up to speed.
DeMarco, Lister. Peopleware, 2013. (117-118)RSS