6.5 : 边际产量 II

The marginal product of the variable input labor is MP_L. It is the change in total product from adding labor while keeping capital, such as the number of ovens, constant.

Consider a bakery producing bread. One baker produces 30 loaves of bread a day. With the addition of another baker, the daily output rises to 75. Here, the MP_L is 45.

In the initial stage, the addition of a baker significantly increases the MP_L. For example, with the addition of the second baker, the output increases by 45 units per day. This stage of increasing MP_L  is called the first stage or the stage of increasing marginal returns.

After a certain point, the MP_L  starts to decline. For example, with the addition of the third baker, the output increases by 30 units per day. The decline in MP_L represents the second stage or the stage of diminishing marginal returns.

Eventually, the MP_L becomes negative. This is called the third stage or the stage of negative marginal returns.

The rate at which the MP_L changes is important to understand the stages of production.