While the term “trend” is often used in the study of demographics, I have chosen not to use the term because of potential confusion with the Twitter term “trending.” While the appropriate term to use to describe “a general direction in which something is developing or changing,” the term “trending” has now taken on a new meaning. “To trend” nowadays is to be the “meme of the moment” (e.g. celebrities, sporting events, extreme weather events). Demography is a study of long-term data sets and analysis and shouldn’t be confused with minute intervals of time.
Instead I will use the term “projections” when addressing demographic and census data that are current, reliable and relevant. While one could argue that the word “projections” implies the future, I argue that since demographic data are based on sampling, the numbers I will refer to are all projections, albeit the best data our government agencies provide. When I reference the term “future projections or projecting” then I am making an educated estimate based on sound research at that given time.
Birth rate is the total number of births per 1,000 of a population each year. The U.S. Census Bureau tracks this annually. Conversely, the mortality rate is the total number of deaths per 1,000 of a population each year.
The rate of natural increase of a population equals the birth rate minus the mortality rate (excluding immigration). Of course, if the mortality rate exceeds the birth rate you have a decrease in natural population.
Fertility rate is the average number of children that could be born to a woman over her lifetime. While this rate is not a factor when calculating the rate of natural increase it is a factor when projecting future populations.
Migration is the physical movement by humans (or animals) from one area to another. Immigration is the movement of people into another country to which they are not native in order to permanently settle there. Also, of particular interest to school leaders is the rate of Interstate Migration, or transiency. There is little emigration from the U.S. to other countries, where the actual intent is to permanently settle elsewhere. The rate of immigration and transiency is of significant study for demographers and educators.