Population versus sample
Whether you are studying statistics in school or working as a statistician, you will be using the words population and sample often.
Therefore, it is important to understand the meaning of these two words and the difference between them really well.
What is a population?
Suppose a statistician is trying to find out the following:
- Number of students living in UK who are able to get an undergraduate degree before the age of 21.
- Percentage of mothers who prefer to breastfeed their children in the United States.
- The prices of all Toyota Camrys sold in a country for the past three years.
- Companies around the world who start their workers with a minimum wage of 14 dollars.
The population is the entire set of students, mothers, Toyota Camrys, or companies.
The population for the above examples is
- All students living in the UK.
- All mothers living in the United States.
- All Toyota Camrys sold in that country.
- All companies.
As you can see, the word population does not refer to just people. It could refer to people or things such as books or cars.
In reality, you may never be able to get in touch with every single mother living in the USA or every single company around the world.
You may not even be able to contact half of all mothers or even one-tenth of all the companies around the world.
This is where sampling or taking a sample is important.
What is sample?
Since it is not always possible to get in touch with all members of a population, research is usually done with only a portion of the population.
For example, a study to find out how many mothers breastfeed their children could be performed with just a few thousand mothers.
In 2009, the estimated number of mothers in the United States was about 85 million.
Suppose you pick 10 thousand mothers to find out who breastfeed their children.
85 million is the population
10 thousand is the sample.
Suppose you want to know the prices of all Toyota Camrys sold in the USA.
There is lots of data here since even if you focus on one single company, the prices may vary a lot.
Suppose that there 50,000 variations of the price.
You pick 300 variations
50,000 is your population
300 is your sample.
In some cases, it may be quite possible to get in touch with every member of the population.
Of course, your population will have to be small in number. Say for instance a school has 5000 students.
5000 is your population.
With some good planning and organization, you may be able to get in touch with all the students in that population.Population versus sample quiz What is a survey?