Year 8 Interactive Maths - Second Edition

## Data

We collect information in order to draw conclusions, to make business decisions or to predict trends.  Information that has been gathered in some way is called data.  We may collect data ourselves or obtain data from an existing source.

### Surveys

The collection of information for a specific purpose is called a surveyData is needed to help solve a problem.  If it is not already available, we collect it by conducting a survey.  The main methods of collecting data are by observation, interview and questionnaire.  Some surveys use a combination of these.

The following terms are often used when we collect data:

###### Population

The population is the whole set of items under consideration.  E.g. If the information on the best selling book in Australia is required, the population is all books on sale in bookshops in Australia.

###### Sample

A sample is drawn from a population.  So a sample is only a part of the population that has been selected to find an information about the population.

For example, a store manager wants to know the favourite washing powder of customers in his area, so that he can stock the more popular items (i.e. different brands of washing powders).  He decides to conduct a survey and choose the first 200 customers as a sample group, asking the question 'what is your favourite washing powder?'

When selecting a sample, two things are taken into consideration:

• The sample should be representative of the population (i.e. it should have the same traits as that of the population).
• All items of the population should have the same chance of being selected for the sample.

If a sample has these two features, it should be a fair representation of the population and unbiased towards particular sub-groups in the population.