statistics

• how to you use random sampling?

  1. assign a number to every member in the sample frame
  2. use a random number generator to create a list of random numbers
  3. match the number to the numbers on the sample frame
• what is stratified sampling?


  gives representation to different groups in a population

  useful when different groups give different results
• what are pros of stratified sampling?


  gives a representative sample when there's easy to define categories

  results can be compared from different groups
• what are cons of stratifies sampling?


  not useful when there aren't easy to define categories

  can be expensive
• what is the method for stratified sampling?

  1. split population into categories
  2. calculate the number to sample from each category
  3. use random sampling to choose the sample members
• what is systematic sampling?


  choosing every nth item

  choose a random start point and take a sample at regular intervals afterwards
• what are pros of systematic sampling?


  should produce an unbiased sample

  can be carried out by a machine
• what are cons of systematic sampling?


  the nth item chosen may coincide with a pattern making the sample biased
• how to use systematic sampling

  1. number all the items
  2. divide the population size by the sample size and use this to choose a random start number
• what is the equation for stratified sampling?


  number in category/total number*sample size
• what is cluster sampling?


  smaller groups in a population is called a cluster

  a random sample of clusters is chosen and every member is included in the sample
• what are pros of cluster sampling?


  it's convenient

  it can save on travel time
• what are cons of cluster sampling?


  it's easily biased e.g. the sample clusters may be similar to each other
• what is quota sampling?


  the population is split into groups

  an interviewer is told to interview a certain number of people from each group
• what are pros of quota sampling?

  it's quick

  gives representation to different groups
• what are cons of quota sampling?


  it's easily biased
• what is opportunity sampling?


  a sample is taken from a section of the populations present at one particular place and time
• what are pros of opportunity sampling?


  it's easy
• what are cons of opportunity sampling?

  it's not representative and biased
• what is judgement sampling?

  researcher uses judgement to choose a sample that represents the population

  useful for researching something specific
• what are pros of judgement sampling?

  it's quick

  may be the only suitable method
• what are cons of judgement sampling?

  researcher could be unreliable

  it can be biased