Under a demographical scope migration is defined as the personal or collective uprooting of cultural values, ideals and traits with the purpose of crossing a geographical barrier in order to settle permanently in a new location.
The difference between the traditional definition of migration and a definition under the scope of demography is the assumption that a demographical definition of migration will include statistics, trends, predictions, and data that will reflect the rate of movement of specific populations, the number of births, deaths, risk factors, and overall every change that has occurred with a migratory group, within a set period of time.
This means that demographers will definitely have a broader scope and a wider spectrum of what really goes on among migratory groups since they keep tabs on data points that no other analyst would have. A demographer, for example, will take into consideration factors in the lives of migratory groups that include births, illnesses, chronic conditions, and deaths, to just name a few. Births and deaths are the two most important indicators, and they are known as fecundity and mortality respectively.
Fertility data looks for the following indicators:
- crude birth rate: how many babies are born each year per 1,000 people
- general fertility rate: how many babies per year among women who can bare children. The assumption here is ages 15-49 or 13-44, depending on the country
- age-specific fertility number of babies per year among specific age groups, per 1,000 women
- total fertility rate: all babies of all fertility groups together
- gross reproduction rate: total number of daughters (because they will reproduce in the future)
- net reproduction rate: total number of daughters for specific age groups
As evidenced on this list, demographers will set their data points within ranges and parameters so that they can take a look at specific periods of time, specific age groups, and specific details, such as gender. This way they can make statistical correlations that can quantify whether one event affects the group, or not.
Mortality rates are determined with these indicators:
- crude death rate: total deaths per year per 1,000 individuals, both genders
- infant mortality rate: refers to yearly deaths of babies under 1 per 1,000 births
- life expectancy: expected years alive
There is a lot of work that goes into demography and not one demographer alone can work all the data points. It is a collective effort to find correlations that are truly statistical.
The way that demographers get their data is from the census that is conducted by different governments to account for the make up of their population. Registration statistics also help to account for the number of bodies in a country. Census for taxation is a method used to find people based on their dues. While these are reliable methods themselves, it is hard to quantify for people who are in a country illegally and have not been counted. When a large population of immigrants arrives in a country without being accounted for, this can also cause a huge impact in the infrastructure of the country because the goods and services are often given on the basis of population and the numbers that the data shows. This is where the data becomes problematic.
This being said, the first issue with getting good counts is the number of immigrants in a country that do not register, or that are not part of the official census. The second is the fact that they also have children, their families multiply and their numbers will not match the statistical official data that is obtained from legal paperwork. These are the key two factors that make demographic migration a very hard subject of study, while it is also a fascinating one.