Population growth reflects food constraints, disease and parental preferences.
In general, higher-income nations now have lower population growth rates. This reflects better availability of contraception, and preferences for later marriages and fewer children. Since birth-rates don't account for the age structure of the population, the US Census calculates a total fertility rate , which is the number of live births the average woman has in her lifetime. The US has been below this rate since 1972. Population Growth and Economic Growth Population growth may increase or decrease economic growth .