Selecting participants

• Sampling is the process of selecting participants from the target population
• Samples should be decent sized and representative of population
• Target population

  A group that a researcher is interested in and wishes to draw conclusions from
• Sampling framework

  • List of individuals within target population
• Types of sampling

  • Random
  • Opportunity
  • Systematic
  • Volunteer
  • Snowball
  • Stratified
• Random sampling

  • Selecting individuals randomly

  + Unbiased improving external validity

  -time consuming and be unrepresentative
• Opportunity sample

  • Recruit people who are readily available

  + Quick and easy to administer

  Less time consuming

  -Biased from small target population

  Unrepresentative lacks external validity
• Snowball sample

  • Current participants recruit further participants via passing of word

  + Enables researcher to locate groups who are hard to access liken drug addicts

  -Not likely to be cross section therefore unrepresentative
• Self-selected or volunteer sample

  • Advertise of study in a newspaper, etc

  + Variety of participants more representative increasing external validity

  -Biased as highly motivated,

  may be non-representative
• Stratified

  • Subgroups within targets identified, participants selected from each strata in proportion to occurance

  +more representative and reduces bias

  -time consuming and difficult to achieve
• Systematic

  • Using a pre-determind system, eg: every 3rd person

  + unbiased

  -not truly unbiased as could be unrepresentative