| 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.
The collection of information for a specific purpose is called a survey. Data 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:
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
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
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
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