Sampling
A method of collecting participants for your research.
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.
Sampling technique
The method used to select people from the population
Bias
In the context of sampling, bias is when certain groups may be over or under represented within the sample collected.
Generalisation
The extent to which findings and conclusions from a particular investigation can be broadly applied to the population. This is possible if the sample of the population is representative of the target population.
Why are sample’s used?
For practical and economic reasons, it is usually not possible to include all the members of the target population so a researcher selects a smaller group, known as a sample.
Why are Sampling technique’s used
To produce a representative sample.
Random sample
A sophisticated form of sampling in which all members of the target population have a equal chance of being selected,
- Researcher gathers the names of all member of the target population and puts them in a hat
- The researcher then randomly picks names out of the hat
- All names picked out will form the sample
Strengths of random sampling
- No researcher bias as the researcher has no influence on the participants picked so they would not be able to choose who they’d like to take part in the study. There’s no control of who the randomly chosen participants are going to be so the researcher cannot choose those who they think will support the hypothesis (no investigator effects).
Weaknesses of random sampling
- Time consuming to find names which would require the gathering of the names of all member of the target population
- It is possible that by chance every participant picked may be a specific type of participant e.g every name picked out is a male. Therefore the sample might not be representative of the target population.
*Exam tip: compare evaluations to other methods if it worth a lot of marks
Systematic Sample
When every nth member of the target population is selected.
- The researcher gathers the names of all the member of the target population and puts them in order e.g alphabetically
- Researcher will then generate a random number to act as the nth term
- This is done by dividing the number of participants in the target population by the number of participants required in the sample
- Researcher then decides a starting point on the list from which to begin collecting participants for the sample. This can be done by using a random number generator between 1-5. The researcher should begin collecting participants from the person on the list who corresponds with the number generated.
- Researcher will then go through the list from that individual and select every nth number of the target population on the list.
- They will keep doing this until they have as many participants as required.
Advantages of Systemic sample’s
- No researcher bias as the researcher cannot personally pick participants they would like to take part in the study. There’s no control of who the randomly chosen participants are going to be so the researcher cannot choose those who they think will support the hypothesis (no investigator effects).
Disadvantages of systemic Sampling
- Finding the target population and putting them in order takes time as it would require the gathering of the names of all member of the target population.
- It is possible that by chance every participant picked may be a specific type of participant e.g every nth member selected from the list may be a male. Therefore the sample might not be representative of the target population.
Stratified Sample
A sophisticated form of sampling form of in which the composition of the sample reflects the proportions of people in certain sub-groups (strata) within the target population or the wider population.
- Researcher work out the proportion of groups in the target population
- They then try to replicate these proportions within a sample e.g if 60% of the target population is female then 60/100 participants in the sample will be female.
- To do this, the researcher will gather the names of all members of the target population and split them into groups e.g all females names go into one hat.
- Researcher will then randomly pick out however many participants they require from each hat e.g 60 from female hat and 40 from male hat.
Advantages of Stratified sampling
- The only sampling technique which produces a truly representative sample which accurately reflects the composition of the target population. As a result, the findings from such a sample will be generalisable to the target population.
Disadvantages of Stratified sampling
- Calculating the proportions of groups within the target population can be very time consuming. Furthermore, finding participants in line with the generated proportions may be problematic if the proportion is small and thus participants are difficult to get ahold of.
Opportunity sampling
Researcher chooses participants who are members of the target population and are willing and able to take part. This is done by approaching and asking members of the target population if they would like to part take. The researcher continues until they have the desired amount of participants.
Strengths of opportunity sampling
- It is the easiest and most convenient method as you use the first participants you find which means it is less time and effort consuming to acquire your sample than other techniques
Weaknesses of opportunity sampling
- Less representative than other methods as it will only reflect those who are in the same vicinity as where the researcher sought the participants. It will only reflect members of the target population who were present at the time. If it is less representative then the findings will be less generalisable to the target population.
- The sample may be biased as the investigator has full control over who they choose to be a part of the sample. They may pick participants that they think will support their hypothesis. Decrease validity.
*exam tip for whole of research methods: apply when the question says “this study”.
Volunteer sample
Involves participants selecting themselves to be part of the sample
- Researcher will advertise the opportunity to take part in the study on relevant websites, newspapers ad appropriate locations.
- Upon seeing the advertisement, participants themselves contact the researcher if they’re interested
- Those who contact the researcher then form a sample
Strengths of volunteer sampling
- It is relatively a quick and easy method of sampling compared to other methods such as ? sampling because it doesn’t require a lot of initial work, for example collecting names for all members of the target population.
Weaknesses of volunteer sampling
- The sample may attract atypical respondents. Only those interested in the study’s aims will offer to take part. This may lead to atypical results which cannot be generalised to the target population.
- Results may not be generalisable based on where the researcher advertises e.g if the study was advertised in the local newspaper, it will only lead to participants from the local vicinity thus the sample will not be representative so findings cannot be generalised to the target population.
