At optimum population level, a country has its highest output per head. Optimum population level refers to the size of population that can be supported by the available resources in a country without putting undue strain on the resources. When a country reaches its optimum population level, the available resources are utilized efficiently, resulting in higher productivity and output per capita. This means that each individual is able to produce more goods and services, which translates to higher standards of living for the population as a whole.