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Population: when you carry out an investigation to find out information about a group of things or people, this group is known as the population.

Some examples of different populations are:

all the people who live in New York

all the books in a library

all the trees in a forest

all the nurses in a hospital

Glossary

population If you refer to a particular type of population in a country or area, you are referring to all the people or animals of that type there.

Census: you would need to carry out a census if you want to find out information about every member of a population. It is easier to carry out a census if you have a small number of people or things in your population, but if the population is very large then it is usually time-consuming, often expensive and sometimes impractical.

For example, if a biscuit manufacturer that bakes thousands of biscuits every day decided to find out how easily their biscuits break, a census would involve breaking every biscuit that they make. This would be impractical because the population is too big and it would be very time-consuming to test each biscuit individually.

Sampling: instead of carrying out a census of the whole population, you could decide to ask questions or observe just a small group of the things or people within that population. This is called sampling. Using a sample can be a lot less expensive, quicker and much easier than carrying out a census. When you have collected information from a sample, it is then possible to draw conclusions and make estimates about the entire population.

For example, the biscuit manufacturer in the previous example could use a sample to find out how easily their biscuits break by choosing 100 biscuits of different varieties for testing.

Glossary

census A census is an official survey of the population of a country that is carried out in order to find out how many people live there and to obtain details of such things as people’s ages and jobs.

sample A sample of people or things is a number of them chosen out of a larger group and then used in tests or surveys, or used to provide information about the whole group.

Exercise 5

For the investigations listed in the table below, describe the population and decide if it would be practical or impractical to carry out a census to find out information on the whole population.

Investigation	Sample population	Census: practical or impractical?
1 Finding out how many hours of homework are completed each week by the pupils in a specific class in a school.
2 Finding out the number of pets that are owned by adults in London.
3 Finding out the number of pages in each book in a large library.
4 Finding out how many children in the UK walk to school in the morning.