In constant proportion production function , the ratio of factors utilised or in use remain constant . This type of production function is realated to long – run. Long – run signifies that period or duration in which a firm can change all its factors of production. In other words, no factor remains fixed in long- run. Factors of production cannot be classified into fixed and variable factors in the long- run. Scale of production can be completely changed in long – run. A firm has sufficient time to change its factor of production and the scale of production in long – run. In other words, a firm can conveniently change its factors of production in long – run to change its scale of production. So, ratio of factor utilisation remains constant in long – run, only scale of production changes. That is why, long – run production function is also called returns to scale.
