Populations and samples
In research, the word population has a specific meaning. A population is all the people (or animals, plants, or anything else) that researchers are interested in finding out about. A population could be broad, like everyone in the world or everyone in a country, or it could be more narrow, like every woman aged over 60 in a specific town, or every person with cystic fibrosis in a particular hospital.
Researchers are interested in finding out about populations, but in most cases studying everyone in a population would take too long, cost too much or be impossible. Instead of studying the whole population, researchers study smaller samples of people from the population they are interested in. If researchers study a sample of people that is very similar to the range of people within the population, then they can use the sample to make generalisations about the population. A sample that is sufficiently similar to the population in every way that might be important is called a representative sample.
For example, to estimate the Body Mass Index of men aged 26-30 in the United Kingdom, researchers might study a sample of 1,000 British men aged 26-30. If the sample is representative, the researchers can use their findings to make conclusions about the larger population.
There are many different ways to choose research samples, each with their own advantages and disadvantages. For more on this, see Sampling methods.