OPT is part of the economics theory of population.
According to economics, there are five factors of production: land, labor, capital, organization and enterprise.
One single factor produces nothing.
Initially the cost of production falls with increasing use of a factor but it starts increasing thereafter.
Up to the optimum size there are conditions of increasing returns as economics of large scale production is enjoyed by any increase in output. However, beyond the optimum size the diseconomies of large scale production or decreasing returns begin to set in.
Perfect substitution is impossible.
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At the optimum level the ratio of marginal productivity of a factor to the price of that factor is the same for all the factors.
Optimum point is not fixed. It depends on other factors.
OPT gives an objective ideal according to which changes in population should be controlled.
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The limitation of the OPT is that it ignores the distributional aspects of an increase in national income. Moreover, it takes a very narrow and materialistic view of social objectives; maximizing per capita income is not always the goal (Hitler and Mussolini wanted a large population for military power and communist USSR awarded the Order of Lenin to a mother of fourteen children in the interest of the fatherland.
