sampling

• what is meant by population

  a group of individuals a researcher is interested in- a statement will be made
• what is meant by a sample

  a group of people who take part in a research investigation- the sample is drawn from a target population
• what is generalisation

  the extent of which findings and conclusions can be applied to the population
• what is the main limitation of sampling

  bias
• what is bias in the context of sampling

  when certain groups are over-or - underrepresented within a sample selected- this limits the extent to which generalisation can be made to the target population
• what is random sampling

  where all members of a target population have an equal chance of selection- complete list is obtained- all names are assigned a number and a lottery method is used
• what is a strength of random sampling

  less risk of bias- the researcher has no choice over who is chosen as everyone has an equal chance of being chosen- this means the sample higher generalisability because the sample is likely to be representative of the target population
• what is a weakness of random sampling

  generalisability bias- the researcher cannot be certain that the sample is representative as it is difficult to ensure that that everyone in a target population is included in the sample- this leads to a lack of external validity
• what is systematic sampling

  where every nth member of the target population is selected- a complete list is obtained and is organised in some way- a sampling system is nominated and this forms the sample
• what is a strength of systematic sampling

  less likely to be subject to bias- it is likely that a systematic sample is more representative of the target population- the researcher has no choice over who is selected and the sample spread evenly across the population- this increases the generalisability and external validity
• what is a weakness of systematic sampling

  possibility of bias- there is a risk that subgroups within a population could be missed if they never fall within the nth position- this means the sample isn't a fair representation of the population and this reduces the generalisability and external validity
• what is opportunity sampling

  people who happen to be available and willing to take part at the time - the researcher approaches people in the population and this is repeated until they have enough participants
• what is a strength of opportunity sampling

  practical- this allows for a large sample of Ps to be gathered quickly and easily- this makes it a convenient sampling and a cost-effective one
• what is a drawback of opportunity sampling

  potential for bias= the sample is likely to be drawn from a small part of the target population as it will only include people who happen to be around and available

  researcher bias means that they could be biased in who they choose to approach
• what is volunteer sampling

  participants select themselves to be a part of the sampling ( self-selecting sample)
• what is a strength of volunteer sampling

  more ethical- the Ps come to the researcher- they have consented to take part- this means the ethical guidelines with Ps has been upheld
• what is a drawback of volunteer sampling

  potential for bias- it is likely a certain 'profile' or person puts themselves forward to be a part of the sample - this means it could be unrepresentative of the population and it would be difficult to generalise findings
• what is stratified sampling

  where the sample represents the different sub- groups (strata) within the target population

  • identify the different strata
  • work out the proportion of people needed for each strata
  • calculate the number of people needed in the sample for each strata
  • randomly select the correct number of Ps
• what is a strength of stratified sampling

  generalisable- this will be representative of the population because of the effort made which therefore increases the external validity
• what is a weakness of stratified sampling

  less practical- it is expensive and time- consuming to use this method as it requires the researcher knowing all the strata's and this can take time and money- there are negative economic implications