Sampling

• What is the target population?


  the particular group of people the psychologists want to be able to generalise their findings to (need a varied sample to avoid bias, want to be able to generalise findings to improve society)
• What is a sample


  the group of people selected to represent the target population; these are the people studied in research - their behaviour is measured
• What is sampling

  the process of selecting participants from the population
• What is the problem with sampling bias


  it means we're unable to generalise results to the target population
• What are some examples of problems with generalisability


  only studying people from one area, age bias, gender bias or may only be reflective of one type of ethnic origin
• What are the four different types of sampling methods

  • opportunity sampling
  • volunteer/self selecting sample
  • random sampling
  • snowball sampling
• What is opportunity sampling


  making use of people that are "readily available to you (need to say in exam)" and willing to participate
• What is volunteer/self selecting sample

  people who want to take part in research volunteer themselves. psychologists put out an "advert (must say)", - e.g. poster, TV advert, mail etc - people who are interested reply to advert and psychologist filter responses and collect a sample that reflect target population
• What is random sampling

  "every member of the target population has an equal chance of being selected (must say in exam)", the names of all members of the target population + all potential Ps are entered into a draw + names are randomly selected until the desired No of Ps are chosen, Ps then contacted to take part
• What is snowball sampling 


  used if target population is hard to reach e.g drug users, criminals. ask participants to suggest someone else who might be willing or appropriate for study
• What does representative mean


  reflect the target population
• Strengths of opportunity sampling


  Point = is the easiest, quickest and most economical way to obtain participants as the psychologists will use people they have easy access to and they don't have to pay for advertising

  Comment = useful for spending more time exploring the behaviour and analysing results
• Weakness of opportunity sampling

  P= likely to produce a bias sample as only certain types of people will be selected from limited areas; therefore it isn't very representative

  e.g. researcher may select people who look more friendly or willing to participate

  C= reduces generalisability of the behaviour to the target population
• Strengths of volunteer/self-selecting sample


  P= gives a wide range of access to potential participants. due to Ps volunteering themselves, it is also convenient and ethical if it leads to informed consent and people will be less likely to drop out

  C= more representative of the target population as a wider group of people will see the advert
• Weakness of volunteer sampling 


  P= often unrepresentative as it leads to a bias sample, people tend not to respond to adverts etc unless they have a strong interest/view to share or a motivation to take part

  C= lowers the generalisability of the behaviour and can increase volunteer bias/ more likely to respond with DCs
• Strengths of random sampling 


  P= the least bias method of sampling as all members of the target population have an equal chance of being selected (and the researcher doesn't collect them)

  C= making it the most representative sampling method, meaning we can generalise the behaviour to the target population
• Weaknesses of random sampling 


  P= very difficult and time consuming to do, especially with large target populations

  C= limits the potential size so will lead to the sample's behaviour being less generalisable to the target population
• Strengths of snowball sampling 


  P= possible to include members of groups where no lists or identifiable clusters even exist (e.g drug abusers, criminals)

  C= we have representation groups that would otherwise not be researched
• Weakness of snowball sampling 


  P= there is no way of knowing whether the sample is representative of the population

  C= we don't truly know whether we can generalise the behaviour to the target population