Figure19-3The Value of the Marginal Product Curve This curve shows how the value of the marginal product of labour depends on the number of workers employed. It slopes downward because of diminishing returns to labour in production. To maximize profit, Alec and Janet choose the level of employment at which the value of the marginal product of labour is equal to the market wage rate. For example, at a wage rate of $200 the profit-maximizing level of employment is 5 workers, shown by point A. The value of the marginal product curve of a factor is a profit-maximizing producer’s individual demand curve for that factor.