Background of Population
In order to have a better sense of how the US population has grown, here is a graph of the population in the United States based on official data from the government website: https://www.census.gov.
The above image shows the trend of the US population (U.S. Population, 2018). The x-axis indicates the year, and the y-axis shows the size of the population in the United States. People can observe the change in the size of the population in the United States according to this graph as well. For instance, between 1915 and 1920, the population does not increase smoothly.
The size of US population is determined by birth rate, death rate, net migration, and other economic and sociological factors, such as government policy, technology, age, and sex distribution, or economic growth.
The population projection is based on mathematical models such as exponential models or logistic models. Since each model can only consider some factors that influence the size of the population, it has its own limitations. For instance, when people use the logistic model to predict the size of the population in the future, the model only consider limited factors such as birth rate, death rate, initial population size, and the carrying capacity of that region. Carrying capacity is determined by factors such as available resources or average space per person in a certain area. The logistic model will omit some important factors that can influence the size of the population, such as government policies. Historically, researchers replaced old models by developing new and better models. For instance, in general, the logistic model can provide more precise prediction than the exponential model does. The reason is that in addition to the factors that the exponential model takes care of, the logistic model can also account for the carrying capacity of a specific region.
