sampling

• opportunity sampling


  happen to be available so are being recruited conveniently
• opportunity sampling strengths


  time saving and less costly
• opportunity sampling limitations 


  not representative as lacks generalisability and researcher bias due to being in control of who they select
• random sampling


  all members of the population have an equal chance of being selected, a random number generator
• random sampling strengths


  no researcher bias as the researcher has no influence on who is picked
• random sampling limitations


  can be time consuming and volunteer bias as participants can refuse to take part so can end up with an unrepresentative sample
• systematic sampling


  a predetermined system is used whereby every nth member is selected from the sampling frame
• systematic sampling strengths


  avoids researcher bias and usually fairly representative of population
• systematic sampling limitation 


  not truly unbiased unless use a random number generator then starting the systematic sample
• stratified sampling


  the composition of the sample reflects the varying proportions of people in particular subgroups within the wider population
• stratified sampling strengths 


  no researcher bias as the selection within each stratum is done randomly, produces representative data due to the proportional strata hence generalisation is possible
• stratified sampling limitation


  time consuming
• volunteer sampling 


  involves self selection whereby the participant offers to take part either in response to an advert or when asked to
• volunteer sampling strengths


  quick access to willing participants so is easy and time consuming as they are more likely to cooperate in the study
• volunteer sampling limitation


  volunteer bias as they may attract a particular profile of a person and may not take the study seriously