Sampling

• Census 


  Observers or measures every member in a population
• Sample 


  Selection of observations taken from a subset of the population which is used to find out info about the population as a whole
• sampling units 


  individual units of a population
• Simple random sampling 


  Has an equal chance of being selected

  advantage- free of bias

  disadvantage- a sampling frame is needed
• systematic sampling 


  chosen at regular intervals

  advantages- simple and quick to use

  disadvantag- bias
• stratified sampling 


  population is divided into mutually exclusive strata and a random sample is taken from each

  advantage- accurately reflects population

  disadvantage - population must clearly classified into distinct strata
• quota sampling 


  an interviewer or researcher selects a sample that reflects the characteristics of the whole population

  advantage- quick easy and inexpensive

  disadvantage- bias
• opportunity sampling 


  taking as sample from people who are available at the time the study is carried out

  advantage- easy to carry out and inexpensive

  disadvantage- unlikely to provide a representative sample
• continuous variable 


  a variable that can take any value in a given range
• discrete variable 


  variable that can only take specific values in a given range
• cities in uk 


  leuchars

  leeming

  heathrow

  hurn

  cambourne
• cities in world 


  Jacksonville (USA)

  Beijing (china)

  Perth (Australia)