The growth in computerised technology has made it possible to analyse ever larger and more complex data sets, resulting in more efficient, responsive and adaptable processes. It has allowed for advances in a range of fields such as medicine, environmental science, transportation, manufacturing and logistics.
At the same time, data has also been used to influence opinion and create political divisions. It has intruded on personal privacy and created greater inequality. It is increasingly important for us to understand how data is collected and used, and be aware of the impact it may have on our lives and our future.
Population or sample
One decision that has to be made, before data collection begins, is whether to collect data from every member of a population, or to only collect data from a sample of members within that population.
Population and census
In statistics, a population refers to every member within any particular group of interest. It could be the entire population of a country, the population of a school, the number of frogs living in a wetland, the number of trees in a forest, or the number of cars in a parking lot.
A survey conducted on every member of a population is called a census. In Australia, a nation-wide census is conducted every five years by the Australian Bureau of Statistics (ABS). Data obtained from the census is used by the government to plan for the future direction of the country. It is needed for planning purposes for such things as the setting of electoral boundaries and the equitable distribution of resources. Apart from a count of people in each dwelling on census night, questions are asked of each household that are intended to inform public policy making.
Sampling the population
Collecting data from every member of a population is the most accurate way of gathering information, but it is not always the most practical, and can be very expensive. For these reasons, data is often gathered from a smaller group, or sample, that can be used to estimate the characteristics of the wider population.
The size of the sample is an important consideration. If the sample is too large, it may be too expensive or time-consuming to collect the data. If it is too small, the sample may not be representative of the population.
Practice questions
QUESTION 1
State whether the following statement is true or false:
In a sample survey, information is obtained from the entire population.
True
AFalse
B
QUESTION 2
State whether the following is an instance of a sample or a census:
A random selection of some people at a mall.
Sample
ACensus
BA stock take of all the goods in store.
Sample
ACensus
BA crash test of new cars just manufactured by a factory.
Sample
ACensus
BAsking all the teachers at your school whether they approve of a new class timetable.
Sample
ACensus
B
QUESTION 3
For a statistical survey the population is deemed to be all people in a city who play in any organised sporting competition.
Which three of the following are samples of that population?
$500$500 spectators chosen from a weekend sports match.
AThe members of $3$3 teams chosen from the local hockey tournament.
B$100$100 people chosen at random from a local park.
CAll students from a local school who compete in a school sports competition.
DAll the active members of a local football club.
E