# Australian Bureau of Statistics

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 Understanding statistics

Module 1: Producing Data

3. Sources of data > 3.2 Generating your own data > 3.2.1. Understanding population and sample

ii. Sample

Data can be collected from a sample to answer questions about the population. That is to say, information from samples allows us to make inferences (draw conclusions) about the population.

Samples and variation

A feature of samples is that a second sample collected from the same population will be different from the first sample, and so on. This difference between samples indicates the variation that exists within a population.

Statisticians are interested in this difference because it can be used to infer something about a population. The variation in a property or characteristic that exists between units of a population can be measured. The measurements of these properties for each unit are called variables. By using samples, these variables can be compared within a smaller group rather than with the entire population. The results of this comparison can then be inferred for the entire population. Although it is often useful to remember that units or members of a population are more similar than they are different, it is the differences in which statisticians are interested.

 Test your knowledge Question If the members of a population were identical and there was no variation (which is very unlikely), how many members would you need to sample to be able to draw some conclusions about the population? a) 1 b) 10 c) 100 d) 1000 Answer Click here for answers

You might now be starting to realise that it is the variation in a population that influences how that population is sampled.

The relationship between population, unit and variable

Figure 1 - The relationship between population, unit and variable

You might notice that the smiley faces have more similarities than they have differences. However, a question that might be asked is: “Why are some smiley faces more likely to be attacked by predators than others?”

To answer this question you might begin by collecting data from records of deaths. In these records, the colour of the smiley face is one of the variables recorded.

 Test your knowledge Question What sort of evidence are you using here to answer the research question about smiley faces? a) Pre-existing data b) Data that has been made up c) Anecdotal evidence d) Data generated from an experiment or observation Answer Click here for answers