Sampling methods

• Introduction to sampling


  • researchers want to be able to generalise their findings
  • sample should share characteristics of target population
• Target population


  a large group of individuals a researcher is interested in studying
• Sample


  sub-group of the target population that take part in the investigation and is representative of the target population
• Sampling technique


  method used to select participants from a population
• Sampling techniques

  1. random

  2. systematic

  3. stratified

  4. opportunity

  5. volunteer
• Random sampling


  every member of a population has an equal chance of being chosen
• Evaluation of random sampling

  STRENGTHS

  • reasonable chance of getting a representative sample

  WEAKNESSES

  • difficult and time consuming, difficult to obtain
  • may have an unrepresentative sample
  • selected participants may refuse to take part
• Systematic sampling


  involves using a predetermined system to select participants from a population
• Evaluation of systematic sampling

  STRENGTHS

  • objective and avoids researcher bias
  • unbiased

  WEAKNESSES

  • if the list has been assembled in a particular manner, bias may be present
• Stratified sample


  classifying the population into subgroups and choosing a sample which consists of participants from each strata in the same proportions that they occur in the population
• Evaluation of stratified sampling

  STRENGTHS

  • avoids misrepresentation
  • more likely to have high population validity

  WEAKNESSES

  • Takes more time and resources
  • care must be taken to ensure each characteristic is represented
• Opportunity sampling


  researchers select anyone who's available at the time and fits the criteria to participate in the study
• Evaluation of opportunity sampling

  STRENGTHS

  • easy and inexpensive
  • less planning and preparation required

  WEAKNESSES

  • may not be representative
• Volunteer sampling


  participants select themselves to be part of the study
• Evaluation of volunteer sampling

  STRENGTHS

  • often achieves a large sample size
  • Quick, convenient and economical

  WEAKNESSES

  • volunteer bias