Sampling, Chapter 6, 5 Flashcards
What is population?
A group of people who are the focus of the researcher’s interest, from which a smaller sample is drawn
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, i.e. it stands ‘fairly’ for the population being studied
What are sampling techniques?
The method used to select people from the population
What is bias?
In the context of sampling, when certain groups are over- or under- represented within the sample selected.
For instance, there may be too many young people or too many people of one ethnic origin in a sample.
This limits the extent to which generalisations can be made to the target population
What is 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 participants is representative of the target population
What is a target population?
A subset of the general population
What are examples of sample populations?
random sample, systematic sample stratified sample, opportunity sample volunteer sample
What is a random sample?
A sophisticated form of sampling in which all members of the target population have an equal chance of being selected
What is a systematic sample?
When every nth member of the target population is selected (e.g. every 3rd house on a street or every 5th pupil on a school register)
What is a stratified sample?
A sophisticated form of sampling in which the composition of the sample reflects the proportions of people in certain subgroups (strata) within the target population or the wider population
What is an opportunity sample?
Given that representative samples of the target population are so difficult to obtain, many researchers simply decide to select anyone who happens to be willing and available. The researcher simply takes the chance to ask whoever is around at the time of their study (e.g. in the street as in the case of market research)
What is a volunteer sample?
This involves participants selecting themselves to be part of the sample
What are the steps of random sampling?
1) obtain a complete list of all members of the target population
2) All of the names on the list are assigned a number
3) the actual sample is selected through the use of some lottery method ( a computer/ phone randomiser or picking numbers from a hat)
What is produced in a systematic sample?
A sampling frame is produced which is a list of people in the target population organised into, for instance alphabetical order
When is a sampling system nominated?
(every 3rd, 6th, or 8th person, etch)
How may a systematic sample begin?
From a randomly determined start to reduce bias. The researcher then works through the sampling frame until the sample is complete
How do you carry out a stratified sample?
The researcher first identifies the different strata that make up the population
Then, the proportions needed for the sample to be representative are worked out
Finally, the participants that make up each stratum are selected using random sampling
What is an example of a stratified sample?
In Manchester, 40% of people support Man U, 40% support Manchester City, 15% support Bolton and 5% support Leeds.
In a stratified sample of 20 participants, there would be 8 United fans, 8 City fans, 3 Bolton and 1 solitary Leeds supporter
Each of these would be randomly selected from the larger group of fans of their team, e.g. Bolton fans selected Bolton supporters, if there are enough
What is volunteer sample also referred to as?
Self-selection
How does a researcher select a volunteer sample?
A researcher may place an advert in a newspaper or on a common room notice board. Alternatively, willing participants may simply raise their hand when the researcher asks
How does a researcher select an opportunity sample?
The researcher simply takes the chance to ask whoever is around at the time of their study (e.g. in the street as in the case of market research)
What are the strengths of a random sample?
Potentially unbiased so confounding or extraneous variables should be equally divided between the different groups, enhancing internal validity
What are the limitations of a random sample?
Difficult and time-consuming to conduct. A complete list of the target population may be extremely difficult to obtain
You may end up with a sample that is unrepresentative- the laws of probability suggest that random sampling is likely to produce a more representative sample than, say, opportunity sampling
However selected participants many refuse to take part which means you end up with something more like a volunteer sample
What are the limitations of a systematic sample?
Time-consuming and participants may refuse to take part, resulting in a volunteer sample
This sampling method is objective, once the system for selection has been established, the researcher has no influence over who is chosen (even more the case if the start is randomly selected)
What are the strengths of a stratified sample?
Produces a representative sample because it is designed to accurately reflect the composition of the population. This means that generalisation of findings become possible
What are the limitations of a stratified sample?
Stratification is not perfect. The identified strata can not reflect all the ways that people are different, so complete representation of the target population is not possible
What are the strengths of an opportunity sample?
It is convenient. This method is much less costly in terms of time and money than say, random sampling because a list of members of the target population is not required and there is no need to divide the population into different strata as there is in stratified sampling
What are the limitations of an opportunity sample?
They suffer from two forms of bias. First, the sample is unrepresentative of the target population as it is drawn from a very specific area such as one street in one town, so findings cannot be generalised to the target population
The researcher has complete control over the selection of participants and, for instance, may avoid people they do not like the look of (researcher bias)
What are the strengths of a volunteer sample?
Collecting a volunteer sample is easy. It requires minimal input from the researcher (they come to you) and so is less time-consuming than other forms of sampling
The researcher ends up with participants who are more engaged, more so than someone who was stopped on the street
What are the limitations of a volunteer sample?
Volunteer bias is a problem. Asking for volunteers may attract a certain ‘profile’ of person, that is, one who is curious and more likely to try to please the researcher (which might then affect how far findings can be generalised)
