Sampling Flashcards
What is a target population?
A group of people the researcher wishes to apply their findings to
What is a sample?
- A group of people from the target population who will participate in research
- A representative sample is an accurate reflection of the target population
- If unrepresentative, findings can’t be generalised to the target population
How can sampling lead to bias?
- Some sampling types allow researcher influence over who can be selected to participate in the study
- This leads to bias as the researcher may select people of a particular group that they prefer leading to an unrepresentative sample decreasing the validity of results
What is opportunity sample?
- Researcher approaches members of public who are in their target population
- Researcher asks these people if they would like to participate in their study
- If they are willing and able to take part they will form part of the sample
- Researcher continues this process until they have all of the PPs required
What are the strengths and weaknesses of opportunity sampling?
STRENGTHS:
- Easiest and most convenient method of sampling, all the researcher needs to do is go to a location and ask members of the target population to take part. Thus takes less effort than other methods e.g. random
WEAKNESSES:
- May be unrepresentative of TP as it will only be reflective of those inthe vicinity of where the researcher sought PPs and were present at the time the researcher was. Thus findings may not be generalisable to whole TP
- Sample may be biased as researcher has full control over who they choose to be part of the sample thus might select those they believe will support their hypothesis. This decreases the validity of their results
What is volunteer sampling?
- Researcher will advertise opportunity to take part in study on relevant platform
- Upon seeing the advert, PPs may contact the researcher if they are interested
- Those who contact the researcher then form the sample until researcher has enough PPs
What are the strengths and weaknesses of volunteer sampling?
STRENGTH:
- Relatively easy method to use and doesn’t require a lot of initial work compared to other methods like random sampling
WEAKNESSES:
- May attract atypical correspondents. Only those interested in study’s aim will take part in the study. As a result they may try harder in the study due to their interest leading to atypical responses which can’t be generalised to TP
- Results may not be generalisable based on where the researcher advertised e.g. if study is advertised in local newspaper only PPs from that area, thus sample won’t be representative of TP
What is random sampling?
- Researcher gathers names of all members of TP and puts them in a hat
- Researcher picks as many names as required out of the hat
- All names picked out of hat form sample
What are the strengths and weaknesses of random sampling?
STRENGTH:
- No researcher bias - researcher can’t personally pick PPs to take part as they have no control over who the randomly selected PPs will be. Thus can’t select PPs who will support their aim. No investigator effects, increasing validity
WEAKNESSES:
- Requires gathering names of all members of TP which can be very time consuming and inconvenient
- Possible that by chance every PP picked can be a specific type of PP e.g. every name picked out of hat is male. Thus findings may not be representative of TP and so can’t be generalised
What is systematic sampling?
- Researcher gathers names of members of TP and puts them in order e.g. alphabetically
- Researcher then generate an nth term by dividing the TP by sample size
- Then the starting point for the sample is randomly selected by randomly generating a number between 1-5 e.g. if 3 is selected, third person in list = first person in sample
- Researcher then selects every nth person from list until they have enough PPs
What are the strengths and weaknesses of systematic sampling?
STRENGTH:
- No researcher bias - researcher can’t personally pick PPs to take part as they have very little control over who the randomly selected PPs will be. Thus can’t select PPs who will support their aim. No investigator effects, increasing validity
WEAKNESSES:
- Requires gayhering names of all members of TP which is very time consuming and inconvenient
- Possible that by chance every PP picked can be a specific type of PP e.g. every nth person is male. Thus findings may not be representative of TP and so can’t be generalised
What is stratified sampling?
- Researcher works out the proportions of groups within the TP
- Researcher tries to replicate these proportions within the sample e.g. if 60% of TP is female, 60 out of 100 PPs in sample will be female
- To do this researcher gathers all names of members of TP and splits them into groups e.g. all female names in one hat
- Researcher will then randomly select however many PPs they need from each hat e.g. 60 from female hat, 40 from male hat
What are the strengths and weaknesses of stratified sampling?
STRENGTH:
- Only sampling method that produces a truely representative sample which accurately reflectts the composition of the TP. Any research done on such a sample can be generalised
WEAKNESS:
- Working out the proportion of groups within the TP can be very time consuming. Also findings PPs in line with generated proportions can be problematic if the proportion is small and thus PPs are difficult to get a hold of
