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Population and samples

Population and samples

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Summary

Population and samples

​​In a nutshell

When carrying out a statistical survey, different types and amounts of data can be collected. The population is the whole set of the items or individuals that are of interest. A census measures every member of the population. A sample measures only a subset of the population, and these measures are used to estimate measures for the population. There are advantages and disadvantages of using a census and using a sample.



Definitions

There are various definitions you need to know when working with data.


NAME

DEFINITION

Population

The whole set of items or individuals of interest.

Census

A measurement or observation from every member of the population.

Sample

A selection of measurements or observations from a subset of the population.

Sampling units

The individual items or members of the population.

Sampling frame

A list of all the sampling units in the population.

Parameter

A population parameter is a value that can be calculated using the whole population. It summarises everything known about the population.

Statistic

A value that can be calculated from a sample. A statistic can be used to estimate a parameter.


​

Census and sample

If data is collected from the entire sampling frame, i.e. the whole population, it is called a census. A census can be time consuming and expensive, however the information gathered would be representative of the population. It is usually quicker, easier and cheaper to take a sample, but it is important to ensure that the sampling method creates a sample which is representative of the population.

ADVANTAGES

DISADVANTAGES

Census
  • It gives a completely accurate result.
  • It is time consuming and expensive.
  • Cannot be used when the testing process destroys the items in the population.
  • It is difficult to process large quantities of data.

Sample
  • The process is less time consuming and cheaper.
  • Less data to process.
  • It may not give a completely accurate result.
  • The sample may not be large enough to represent the different subgroups of the population.


Example 1

A battery manufacturer wants to test the lifetime of the batteries they make by seeing how long they last. Should they use a census or a sample? Given a reason for your answer.


A census would require all the batteries to be used and they would consequently have no more batteries left to sell.

Therefore, the manufacturer should use a sample.


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Exercises

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FAQs - Frequently Asked Questions

What is a sample?

What is a census?

What is a population?

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