There are two special classes of production functions that are often analyzed. The production function formula_16 is said to be homogeneous of degree formula_17, if given any positive constant formula_8, formula_19. If formula_20, the function exhibits increasing returns to scale, and it exhibits decreasing returns to scale if formula_21. If it is homogeneous of degree formula_22, it exhibits constant returns to scale. The presence of increasing returns means that a one percent increase in the usage levels of all inputs would result in a greater than one percent increase in output; the presence of decreasing returns means that it would result in a less than one percent increase in output. Constant returns to scale is the in-between case. In the Cobb–Douglas production function referred to above, returns to scale are increasing if formula_23, decreasing if formula_24, and constant if formula_25.