SAMPLES AND SAMPLING TECHNIQUES

• WHAT IS SAMPLING?

  process of experiment participants being selected to represent a target population for research purposes
• WHAT MUST A SAMPLE BE?

  representative of target poplulation
• SAMPLING TYPES?

  • random
  • systematic
  • stratified
  • opportunity
  • volunteer
• WHAT DOES RANDOM SAMPLING MEAN?

  everyone in target population has an equal chance of being selected
• HOW DOES RANDOM SAMPLING HAPPEN?

  1. Entire target population must be listed and numbered
  2. All numbers put into a hat
  3. Numbers are selected out of the hat without looking
  4. Until researcher reaches their sample size
  5. Participants who match that number are selected
• HOW DOES SYSTEMATIC SAMPLING HAPPEN?

  1. Entire target population listed and ordered
  2. Every nth person selected
  3. Nth term depends on sample size required
• HOW DOES STRATIFIED SAMPLING HAPPEN?

  1. Sampling frame divided into categories (strata)
  2. Participants selected from each strata
  3. In same proportion to population
• HOW DOES OPPORTUNITY SAMPLING HAPPEN?

  1. Researchers select first available bodies
  2. Usually those available at time of study/ most convenient
  3. This method is easy and time efficient for the researcher
• HOW DOES VOLUNTEER SAMPLING HAPPEN?

  1. Researcher advertises study
  2. Collect their sample from people who respond
  3. Self-selection requires minimal input from researcher
  4. Creates biased sample
  5. Results less generalisable
• ADVANTAGES OF RANDOM SAMPLING?

  • equal chance of all individuals being selected
  • eliminates sampling/ researcher bias
• DISADVANTAGES OF RANDOM SAMPLING?

  • time-consuming
  • requires full list of target population
  • can still pick out similar participants
  • some may refuse
• ADVANTAGES OF SYSTEMATIC SAMPLING?

  • avoids researcher bias
  • quite representative
• DISADVANTAGES OF SYSTEMATIC SAMPLING?

  • difficult to achieve
  • costly
  • time-consuming
  • some may refuse (list must be edited and re-ordered)
• ADVANTAGES OF STRATIFIED SAMPLING?

  • accurately represents target population
  • more generalizable data
  • decreased researcher bias (random from subsets)
• DISADVANTAGES OF STRATIFIED SAMPLING?

  • time-consuming
  • extremely difficult (every variable must be considered)
  • individual differences within stratas
• ADVANTAGES OF OPPORTUNITY SAMPLING?

  • easy
  • convenient (both researcher and participants)
• DISADVANTAGES OF OPPORTUNITY SAMPLING?

  • decreased population representation
  • participants usually have similar characteristics
  • prevents generalisation
• ADVANTAGES OF VOLUNTEER SAMPLING?

  • quick
  • easy
• DISADVANTAGES OF VOLUNTEER SAMPLING?

  • volunteer bias
  • study made up of participants with similar characteristics
  • prevents generalisation
• IS RANDOM SAMPLING REPRESENTATIVE?

  somewhat/ usually
• IS SYSTEMATIC SAMPLING REPRESENTATIVE?

  quite
• IS STRATIFIED SAMPLING REPRESENTATIVE?

  very
• IS OPPORTUNITY SAMPLING REPRESENTATIVE?

  no
• IS VOLUNTEER SAMPLING REPRESENTATIVE?

  no
• IS RANDOM SAMPLING PRACTICAL?

  no
• IS SYSTEMATIC SAMPLING PRACTICAL?

  no
• IS STRATIFIED SAMPLING PRACTICAL?

  no
• IS OPPORTUNITY SAMPLING PRACTICAL?

  yes
• IS VOLUNTEER SAMPLING PRACTICAL?

  yes
• IS RANDOM SAMPLING FREE FROM BIAS?

  yes
• IS SYSTEMATIC SAMPLING FREE FROM BIAS?

  yes
• IS STRATIFIED SAMPLING FREE FROM BIAS?

  yes
• IS OPPORTUNITY SAMPLING FREE FROM BIAS?

  no
• IS VOLUNTEER SAMPLING FREE FROM BIAS?

  no
• WHAT SAMPLING TECHNIQUES ARE REPRESENTATIVE?

  random, systematic and stratified
• WHAT SAMPLING TECHNIQUES ARE PRACTICAL?

  opportunity, volunteer
• WHAT SAMPLING TECHNIQUES ARE FREE FROM BIAS?

  random, systematic, stratified