Sampling

• Define sampling?


  When a researcher needs to decide how they select participants to take part in their investigation
• Define population?


  A group of people from whom the sample is drawn
• What are the sampling methods?


  opportunity, random, systematic, stratified and volunteer
• Explain opportunity sampling?


  When participants happen to be available at the time which the study is bring carried out so are recruited conveniently
• Explain random sampling?


  When all members of the population have the same equal chances of being the one that is selected, each member of the population is assigned a number, then the lottery method/ random number generator is used to randomly choose the sample
• What is systematic sampling?


  A predetermined system is used where every nth member is selected from the sampling frame. The numerical selection is applied consistently
• Define stratified sampling?


  When the composition of the sample reflects the varying proportions of people in certain sub groups (strata) within the wider population
• What is the method in stratified sampling?

  1. identify the strat
  2. Calculate the required proportion needed for each stratum based on target population
  3. Select a sample at random from each stratum using a random selection method
• Define volunteer sampling?


  It involves self selection where the participant offers to take part either in response to an advert/ when asked to
• What is a strength of opportunity sampling?


  It is an easy method of recruitment which is time saving and less costly
• What is a strength of random sampling?

  There is no researcher bias, the researcher has no influence of who is picked
• What is a strength of systematic sampling?


  It avoids researcher bias and is fairly representative of the population
• What is a strength of stratified sampling?


  No researcher bias as the selection within each stratum is done randomly, it also produces representative data due to the proportional strata so generalisation is possible
• What is a strength of volunteer sampling?


  It allows quick access to participants which makes it easy and not time consuming as participants are willing to take part they are more likely to co operate in the study
• What are the limitations of opportunity sampling`?


  • It is not representative of the whole population so lacks generalisability
  • Researcher bias is presented as they control who they want to select
• What are the limitations of random sampling?


  • Time consuming- the researcher has to have a list of the members of the population and then contacting them can take time
  • Volunteer bias- participants can refuse to take part so can end up with an unrepresentative sample
• What is meant by a sampling frame?


  a list of the members of the population
• What are the limitations of systematic sampling?


  It is not truly unbiased unless you use a random number generator and then start the systematic sample
• What are the limitations of stratified sampling?


  • It is time consuming to identify strata and contact people from each
  • A complete representation of the target population is not possible as the identified strata cannot reflect all the differences between people of the wider population
• What are the limitations of volunteer sampling?


  • Volunteer bias- the study may attract a particular profile of a person so generalisability could be affected
  • Motivations like money could be driving participation so participants may not take study seriously which can influence results