sampling

• population? 


  group of people who are the focus of who are the focus of the researchers interest from which a smaller sample is drawn
• sample? 


  group of people who take part in a research investigation. sample drawn from target population and presumed to be representative of that population
• bias? 


  when certain groups are over- or under- represented within the sample selected. limits the extent to which generalisations can be made to target population
• generalisation? 


  extent to which findings and conclusions from a particular investigation can be applied to population. possible if sample of participants is representative of target population
• random sample ? 


  all members of target population have equal chance of being selected.

  1.obtain list of all members of target population

  2. assign all names on list a number

  3.select actual sample through use of lottery method
• systematic sample? 


  when every nth member of the target population is selected.

  sampling frame is produced which is a list of people in target population organised into e.g. alphabetical order. sampling system nominated and may begin from a randomly determined start to reduce bias
• stratified sample ? 


  form of sampling where composition of sample reflects proportions of people in certain subgroups within target population. form of sampling where composition of sample reflects proportions of people in certain subgroups within target population.

  -researcher identifies different strata that make up the population

  -proportions needed for sample to be representative worked out

  -participants that make up each stratum selected using random sampling.
• opportunity sample? 


  researchers decide to select anyone who happens to be willing and available. researcher simply takes the chance to ask whoever is around at the time of their study
• volunteer sample? 


  involves participants selecting themselves to be part of sample.

  to select volunteer sample researcher may put advert in newspaper or willing participants may simply raise their hand when researcher asks
• strength of random sample?

  unbiased as CVs and EVs should be equally divided between groups enhancing internal validity.
• limitation of random sample?

  difficult and time consuming to conduct as complete list of target population hard to obtain

  could end up with a sample thats unrepresentative

  selected participants may refuse to participate
• strength of systematic sampling?

  objective as when selection established researcher has no control who's chosen
• limitation of systematic sampling?

  time consuming and participants may refuse to take part
• strength of stratified sampling?

  produces a representative sample as designed to accurately reflect composition of population so generalisation of finding becomes possible.
• limitation of stratified sample?

  stratification isn't perfect as identified strata can't reflect all the ways people are different so complete representation of population isn't possible
• strength of opportunity sample?

  convenient. less expensive and time consuming
• limitation of opportunity sample?

  suffer from two forms of bias. first, samples unrepresentative of target population as its drawn from a very specific area so findings can't be generalised to target population. secondly, researcher has complete control of selection of participants and may avoid people they don't like the look of (researcher bias)
• strength of volunteer sampling?

  requires minimal input from researcher and is less time consuming. researcher ends up with people who are more engaged
• limitation of volunteer sample?

  volunteer bias. asking for volunteers may attract a certain profile of a person that is one who is curious and more likely to try please the researcher