The statistical population is a random variable related to the objects or individuals to be studied in an investigation. Each of the elements of the population is called an individual and they share some characteristics.
A statistical population can be a group of actually existing objects / people (for example, the set of all the people of a town) or a hypothetical and potentially infinite group of objects conceived as a generalization (for example, the set of all plays possible in chess).
When the number of individuals in the population is large and a study is to be carried out, the population is divided into samples , which are small groups that have characteristics similar to the general population.
Generally, the adjective target population is added, since it is the population on which you want to obtain a specific result.
It is important that this population is delimited in terms of time (a specific period of time: years, months, days, hours, minutes, etc.), and space (a continent, a country, a neighborhood, etc.).
In statistics, this sample must be representative of the population from which it is drawn. In this way, the results obtained with it can be extrapolated to the rest of the population by statistical inference.
The qualities that describe that population for research purposes are called statistical variables and can be qualitative or quantitative.
On the other hand, there is the term population of observations, referring to the set of values that a statistical variable can have in the target population. This means that a single population can have many observation populations.
The 8 main types of statistical population
According to the number of individuals that make up the statistical population, these could be classified into:
1- finite population
It refers to groups of individuals in a clearly defined quantity, such as the inhabitants of a city, balloons in a swimming pool, boxes in a warehouse, among others. They can be counted and grouped.
Some examples of this type of population would be:
- Number of students in a university.
- Number of cars sold during 2017.
- Earthquakes of magnitude greater than 4 ° on the Ritcher scale occurred in a city.
2- Infinite population
They are immeasurable populations. However, it is a purely conceptual notion, since every population is composed of objects or individuals in finite quantities.
Among the cases of infinite population we could mention as examples:
- Grains of sand on a beach
- The number of waves that crash against a reef in one day.
- The drops of water that fall during a rain.
3- Real population
It is the group of concrete elements, such as: the number of people of productive age in Latin America .
Other examples could be:
- The number of users of a given mobile application.
- The number of civil protests in a city during a month.
- The chapters of a television series.
As can be seen, these examples are, at the same time, those of a real and finite population.
4- Hypothetical population
It is a concept that applies when you are working with possible hypothetical situations. For example, how many people could survive a catastrophe.
It is related to the population of hypothetical observations that occurs when working with samples of observations referring to psychological concepts such as anxiety , fear, etc.
In this case, the population of observations is hypothetical, potential.
Example of this would be:
- The level of anxiety that drug addicts would have if they voluntarily follow a specific treatment.
- The level of fear that people may feel when going through a specific experience.
- The anguish a mother can feel after losing her child at an amusement park.
5- Stable population
This is the name given to the groups of elements that keep their qualities almost intact for a long period.
Some examples of these cases have to do, for example, with:
- Changes in the geology of a territory
- Movement speed of the stars
6- unstable population
The qualities of this type of population vary constantly.
7- Dependent population
It is the type of population that changes its values for a defined reason, an identified cause. The dependency can be total or partial.
An example of this could be:
- The level of sales of a product that may depend on: the quality of the product, advertising, distribution, etc.
8- Polynomial population
We speak of a polynomial population when there is interest in several of its characteristics in the research.
For example: a population census generally collects information on different variables of the inhabitants (age, location, level of income and education, etc).
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