Maths

• Census

  Every member is sampled

  Advantage: very accurate

  Disadvantage: expensive anc time consuming
• Sample survery

  Advantage: quick and cheap, easier data collection

  Disadvantage: less accurate, less representative and biasness
• Stratified Advantages

  • Guarantees proportional representation of groups within population
  • Most representative
  • Structure of sample reflects structure of population
• Stratified disadvantages

  • Sampling within each group may suffer disadvantages of simple random sampling
  • You need to know the structure of population
• Simple random

  • Quick
  • Cheap
  • All units have an equal chance of selection
• Simple random

  • Can introduce bias
  • Sampling frame needed
• Systematic

  • Get a list of workers
  • Choose one of the first ten workers at random
  • Choose subsequent 10th worker
• Quota

  • Decide categories
  • Set a quota for each in proportion to their numbers in population
  • Interview workers until quota are full
• Random number

  • Allocate numbers between 1 and 120 to each pupil
  • Use random number generator to select 15 different pupil
• Opportunity

  • Cheap
  • Easy to carry out
  • Not random