Sampling

• What is the difference between a sample, a target population and a population?

  Sample = a subset of a larger group or population that is studied to draw conclusions about the entire group.

  
  

  Target population = specific group of people that an investigation is concerned with

  
  

  Population = large group of people you are interested in studying

  
• Define random sampling (give an example) and its strengths and weaknesses

  A technique in which 100% of the target population has an equal chance of being part of the sample. E.g. Putting all the names into a hat and pick out as many as you need.

  
  

  (+) (unbiased samples)

  (-) (slow and inconvenient to carry out)

  (-) (unrepresentative of population)
• Define systematic sampling (give an example) and its strengths and weaknesses

  Selecting every nth person. E.g. Take all of the named, place them in alphabetical order and choose every nth person until you have enough

  (+) (unbiased samples)

  (-) (slow + inconvenient to carry out)

  (-) (unrepresentative of population)

   
• Define stratified sampling (give an example) and its strengths and weaknesses

  A technique that ensures subgroups of the target population are proportionally represented in a sample. E.g. if 65% of the target population is female, then 65% of the sample should be female

  (+)(Most representative of population)

  (+) (unbiased samples)

  (-) (very slow and inconvenient to carry out)
• Define opportunity sampling and its strength and weaknesses

  A technique that recruits participants who are readily available at the time by asking people who walk past you in public

  
  

  (-) (Experimenter bias + potential volunteer bias)

  (+) (quick and convenient)

  (-) (unrepresentative of population)
• Define volunteer sampling and its strengths and weaknesses

  A technique that asks for participants by placing adverts for volunteers. 

  
  

  (-) (Volunteer bias)

  (+) (Quick and convenient)

  (-) (Unrepresentative of the population)