sampling

• what is a population?


  everyone who you could study
• why does a sample have to be representative?

  so that your findings can be generalised
• what is a sample?

  a group of people who take part in a research investigation. The sample is drawn from a (target) population and is presumed to be representative of that population.
• what is generalisation?


  the extent to which findings and conclusions from a particular investigation can be broadly applied to a population
• what is bias in the context of sampling?

  When certain groups are over/under represented within the sample selected. This limits the extent to which generalisations can be made to the target population
• what is random sampling?

  where all members of a target population have an equal chance of being selected
• what is the method of random sampling?

  -a complete list of all members of the target population is obtained

  -all names on the list are assigned a number

  -the sample is generated using a lottery method
• what are the strengths of random sampling?

  -less risk of bias- the researcher has no choice over who is chosen

  this means that it could have higher generalisability
• what are the weaknesses of random sampling?

  -issues with generalisability- it is difficult to ensure everyone in the target population is included in the sample

  this could lead to a lack of external validity
• what is systematic sampling?

  where every nth member of the target population is selected
• what is the method of systematic sampling?

  -a complete list of all members of the target population is organised in some way (e.g alphabetically)

  -a sampling system is nominated (decision of what n equates to) ( n could be 'randomly decided each time, to have intervals of different sizes, to reduce bias)

  -sample is generated.
• what are the strengths of systematic sampling?

  -less likely to be subjected to bias- it is likely that a systematic sample is more representative of the target population, because the researcher has no choice over who is selected, and the sample is spread evenly over the population

  this increases the generalisabilty and external validity of findings
• what are the weaknesses of systematic sampling?

  -possibility of bias- subgroups within a population could be missed

  this reduces the generalisability and external validity of findings
• what is an opportunity sample?

  people who happen to be available and willing to take part at the time the researcher wishes to carry out their research
• what is the method of opportunity sampling?

  -researcher approaches people in the population to ask if they will take part in their study

  -researcher repeats this until they have enough participants
• what are the strengths of opportunity sample?

  -practical- a larger number of participants can be easily recruits

  this makes it convenient and cost effective
• what are the weaknesses of opportunity sample?

  -potential for bias- likely to be drawn from a small part of the target population who happen to be available when the research is being conducted. They could also be biased in who they chose to approach

  The sample is unlikely to be representative of the target population, so it is more difficult to generalise the findings.
• what is volunteer sampling?

  participants select themselves to be part of the sample (self-selecting sample)
• what are the strengths of volunteer sampling?

  -more ethical-participants come to you, so they have consented
• what is the method of volunteer sampling?

  researcher asks for volunteers (either in a newspaper advert or online) and then this is thier sample
• what are the weaknesses of volunteer sampling?

  potential for bias- a certain profile of person ( e.g someone with spare time), would put themselves forwards for research

  this means it can be unrepresentative of the target population- hard to generalise
• what is stratified sampling?

  Where the composition of the sample reflects the proportions of certain sub groups (strata) within the target population
• what is the method of stratified sampling?

  -Identify the strata that make up the population

  -Work out the proportions of each strata within the population in percentages

  -Given the sample sided needed, calculate the number of people needed to make up each strata within the sample

  -Randomly select the correct number of participants for each strata from the population
• what are the strengths of stratified sampling?

  Generalisable it is likely that the sample obtained will be representative of the target population because of the effort made to include each relevant strata within the target population in the sample. This makes it more externally valid.
• what are the weaknesses of stratified sampling?

  It’s less practical because it is time-consuming and expensive it also realise on the percentage of groups. This means it has more negative economic implications.