1.1 Populations and samples

• A population is the whole set of items that are of interest.
• A census observes or measures every member of a population.
• A sample is a selection of observations taken from a subset of the population which is used to find out information about the population as a whole.
• Advantages of a census

  • It should give a completely accurate result.
• Disadvantages of a census

  • Time consuming and expensive
  • Cannot be used when the testing process destroys the item.
  • Hard to progress large quantity of data
• Advantages of a sample

  • Less time consuming and expensive than a census
  • Fewer people have to respond
  • Less data to process than in a census
• Disadvantages of a sample

  • The data may not be as accurate
  • The sample may not be large enough to give information about small subgroups of the population
• What is a sampling unit?

  Individual units of a population
• Often sampling units of a population are individually named or numbered to form a list called a sampling frame.