marginal productivity　

marginal productivity　边际生产力，增量差额生产能力　

An increment in total dollar value（or physical quantity）which results from a one-unit increase in the amount of a factor of production employed in any program or process.The successful measurement of the marginal productivity of any factor of production can be attained only when it is possible to isolate its variations from other causes of yield variation.In particular，all other factors of production must be approximately constant at known levels before yield variations can be imputed，with any validity，to the factor in question.