The Federal Acquisition Regulation tells U.S. government buyers how to describe the services they purchase. They should state “the required results rather than either ‘how’ the work is to be accomplished or the number of hours to be provided.”
Such contracts must include “Measurable performance standards (i.e., in terms of quality, timeliness, quantity, etc.),” a method for “assessing contractor performance against performance standards,” and “Performance incentives where appropriate.”