Sampling

• Your sample needs to be representative of the target population, needs to consider different ppt variables
• Random - every member of the target has an equal chance of being selected, highly controlled
• Random sampling AO3:

  Strengths - free from researcher bias, highly controlled, everyone has equal chance

  Limitations - difficult and time consuming, need to complete list of population, could end up unrepresentative
• Representative sample - subset of target group with a similar distribution of relevant characteristics, in turn allowing us to generalise from sample to the target with justification
• Opportunity - anyone who is available and agrees to take part in the research can become a ppt.
• Opportunity sampling AO3:

  Strengths - quick and easy to do, saves money and effort

  Limitations - biased, might not be enough ppts, unrepresentative as ppt are from specific area, lacks generiliseability
• Volunteer - where ppts self-select themselves and choose to take part if research
• Volunteer sampling AO3:

  Strengths - easy, less consuming

  Limitations - volunteer bias, it may attract certain type of people, lacks generiliseability
• Systematic - select every n-th number of the target group, list order has been randomised
• Systematic sampling AO3:

  Strengths - unbiased, gives representative sample, free from researcher bias

  Limitations - doesn't give an equal chance of selection to each individual
• Stratified - the composition of the sample reflects the proportion of people in certain sub-groups (strata) within the target population:

  work out proportion of people needed for each strata, select ppt via random sampling
• Stratified sampling AO3:

  Strengths - free from researcher bias, mainly representative of target population, results can be generalised

  Limitations - cannot represent all the ways in which people are different, so not completely representative
• Validity - assumes that the test measures precisely what it aims to measure, meaning the data collected is accurate
• Single Blind Procedure - ppt doesn't know in what condition they were put in, neither the aim
• Double Blind Procedure - researcher doesn't know either, only collects data