Sampling Flashcards
Whats a Target Population?
target population – a group of people that share a set of characteristics about which the researcher wishes to draw conclusions.
What is a representative sample?
representative sample – a group typical of the target population (i.e. it shares characteristics despite its smaller size) – and generalise findings from the sample to the rest of the population.
Random sampling
What does it mean and how does it work?
Each person in a given population stands an equal chance of being selected.
This means that it is necessary to have the names of every person in the target population. The sample could then be selected by drawing names out of a hat or by entering all the names into a computer random generator and clicking ‘select’ the number of times for participants needed.
Systematic sampling
What does it mean and how does it work?
In systematic random sampling, the researcher first randomly picks the first participant from the population. Then, the researcher will select each n’th participant from the list.
For example, the researcher has a population total of 100 individuals and need 12 participants. He first picks his starting number, 2. Then the researcher picks his interval, 3. The members of his sample will be individuals 2, 5, 8, 11 etc.
A random and a systematic sample is potentially?
There is also reduced researcher?
A random and a systematic sample is potentially unbiased.
As everyone in the target population has an equal chance of being selected, the laws of probability would suggest that the sample should be overall representative of the target population.
There is also reduced researcher bias.
As it is the selection technique itself (e.g. a computer random number generator) that selects the participants rather than the researcher themselves, this means that the researcher is not selecting certain participants only – they are objective sampling techniques
Random and Systematic sample
You may still end up with a?
These sampling techniques can be ?
You may still end up with a biased and unrepresentative sample.
There is always the possibility of accidental bias – while random and systematic sampling is more likely to produce a representative sample, it is not guaranteed to.
These sampling techniques can be difficult and time-consuming.
For example, a complete list of the target population can be difficult to obtain.
Selected participants may refuse to take part.
Stratified sample
What does it mean and how does it work?
Involves dividing the target population into important sub-categories and randomly selecting participants within each sub-category in proportion that they occur in the population.
For example, if 40% of my target population is male and 60% are female, then my sample needs to reflect these proportions.
A stratified sample is going to provide us with the most?
There is also reduced researcher?
A stratified sample is going to provide us with the most representative sample.
This is because there is a proportional representation of subgroups and therefore findings can be generalised to the target population.
There is also reduced researcher bias.
As it is the selection technique itself (e.g. a computer random number generator) that selects the participants rather than the researcher themselves, this means that the researcher is not selecting certain participants only – this is another objective sampling techniques.
Stratified sampling is very?
It will still not provide you with a fully?
Stratified sampling is very time-consuming.
Not only do you have to obtain a complete list of the target population, which, as we have said, can be difficult, you then have to identify the subgroups and calculate proportions.
It will still not provide you with a fully representative sample.
Even though it will provide you with the most representative sample compared to all other sampling techniques, it is still likely that there will be some bias as not all subgroups or strata can be identified.
Opportunity sampling
What does it mean and how does it work?
Involves the researcher selecting anyone who is available at the time.
For example, the researcher uses whoever is around at the time of their study, e.g. in the street.
An opportunity sample is appropriate to use when the sampling frame is unknown.
An opportunity sample is a convenient method of?
It is appropriate to use when the sampling frame is unknown. For example, if you want to research people in a public area such as a shopping centre, you won’t know who will be there at the time, so random, systematic and stratified sampling cannot be used.
An opportunity sample is a convenient method of gaining participants. This is because:It is less costly than random, systematic and stratified sampling because you do not need to source a complete list of your target population It is less time consuming than stratified sampling because you do not need to identify subgroups and work out proportions
Opportunity sampling is likely to result in a?
Opportunity sampling is likely to result in a biased sample.
It is drawn from a small section of the population who are at the same places at the same time and are likely to share similar characteristics, e.g. people who go to the shopping centre on a weekday.
There is an increased chance of researcher bias as they may only approach participants who they think fit their aims / hypothesis
Volunteer sample
What does it mean and how does it work?
Participants select themselves.
For example, in response to an advertisement in a newspaper or poster.
An volunteer sample is a convenient method of gaining?
It is a useful way to locate willing?
It can be seen as a more?
An volunteer sample is a convenient method of gaining participants.
It requires minimal input from the researcher as they come to you.
It is a useful way to locate willing participants.
This means that participants are less likely to drop out.
It can be seen as a more ethical sampling technique.
You are surer that you have consent from participants as they have volunteered for the study (compared to, say, random sampling where participants may feel obliged to take part because they were selected).
Volunteer sampling is likely to result in a?
Volunteer sampling may be more likely to result in?
Volunteer sampling is likely to result in a biased sample.
It is prone to volunteer bias as it may be that only certain types of people are likely to volunteer, e.g. those with a real interest in the topic.
Volunteer sampling may be more likely to result in demand characteristics.
Volunteers may be more eager to help the researcher find evidence to support their aims.
