a) Malthus focused his attention on food production, whereas the optimum theory takes into consideration of economic development in all its aspects.

b) Malthus seemed to be thinking of maximum number for a country, which, if exceeded, would bring misery. According to the optimum theory, there is no rigidly fixed maximum population.

c) According to Malthus, famine, war and disease were the indicators of over population. But the declining trend of per capita output would indicate the over population as per the optimum theory.