Sometimes it is possible to conduct an investigation with every member of the population. This is called a census.
A census of the whole population is taken in Australia every five years. The Australian Census aims to accurately measure the number of people in Australia on a particular night, wherever they are – from Australia's research hubs in Antarctica to remote Indigenous communities in northern Australia.
A census is the most comprehensive way of providing a snapshot of the people of Australia, our key characteristics and where we live. Census data supports planning, decision making and funding at all levels of government, and are behind the services and facilities we use every day.
To explore the data collected by the Census, visit the Australian Bureau of Statistics.
Often it is not possible to carry out a census for the particular population you wish to investigate. It is then necessary to look at a subset of the population. For example, if we want to know what the most popular television show for year 8 students in Melbourne is, the population would be every year 8 student in Melbourne. But it may not be practical to survey every year 8 student, so we could survey some year 8 students from ten Melbourne schools. This is called a sample.