Sampling

What is population?

Population= A group of people who are the focus of the researcher’s interest, from which a smaller sample is drawn- due to reasons such as costs & practicality

What is a sample?

Sample=  small group taken from a (target) population and is presumed to be representative of that population

What are sampling techniques?

Sampling techniques= method used to select people from the population

What are the 5 sampling techniques?

5 sampling techniques=

• random sample (representative)

• systematic sample (representative)

• stratified sample (representative)

• opportunity sample (practical)

• volunteer sample  (practical)

What is random sample?

Random sample= every person in this target population has an equal chance of being selected

• the researcher obtains a list of all the members in the target population and then uses a computerised random generator or the 'names out of a hat' technique to select the required number of participants.

What is the strength of random sampling? 

Strength of random sampling=

• Free from researcher bias- the researcher has no control over who gets selected.

  • confounding or extraneous variables should be equally divided between the different groups, enhancing internal validity.

What are the weaknesses of random sampling?

Weaknesses of random sampling=

• time consuming

• A representative sample is not guaranteed - there is a chance some sub-groups may be over-represented or not selected.

What is systematic sample?

Systematic sample= When every nth member of the target population is selected. A sampling frame (target population) is produced followed by a sampling system (e.g. every 7th person) to obtain the sample.

What is the strength of systematic sampling?

Strength of systematic sample=

• Free from researcher bias- the researcher has no control over who gets selected.

  • is objective. Once the system for selection has been established, the researcher has no influence over who is chosen (this is even more the case if the start is randomly selected)

• A fairly representative sample is obtained.

What is the weakness of systematic sampling?

Weakness of systematic sampling=

• Not entirely unbiased unless the number selected for sampling is chosen randomly, i.e. start with this person and choose every nth person there on.

• time-consuming

• participants may refuse to take part, resulting in a volunteer sample.

What is stratified sampling?

Stratified sampling=

This sample represents a composition of people in certain sub groups (strata) within the target population.

What are the strengths of stratified sampling?

Strengths of stratified sampling=

• Avoids researcher bias.

• The members selected from the sample are randomly selected.

• The sample represents the strata composition.

• accurately reflectthe composition of the population. This means that generalisation of findings becomes possible.

What are the weaknesses of the stratified sampling?

Weaknesses of stratified sampling=

It may lack a 100% representation as individual differences cannot be accounted for.

What is opportunity sampling?

Opportunity sampling=

the researcher selects anyone who is readily available and willing to take part. The researcher simply asks the people who it is most convenient for them to ask e.g. a researcher who also works as a university lecturer may ask students in their seminar group to participate.

What are the strengths of opportunity sampling?

Strengths of opportunity sampling=

Opportunity sampling is convenient. This method is much less costly in terms of time and money than 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 stratifiedsampling.

What are the weaknesses of opportunity sampling?

Weaknesses of opportunity sampling=

-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 is volunteer sampling? 

Volunteer sampling= 

• participants put themselves forwards for inclusion, i.e., they self-select.

• The researcher places an initial advertisement in a magazine/newspaper, on the radio, on the internet/via email, or on a public noticeboard (e.g., a workplace/gym), asking for volunteers to take part in research.

• They may also place questionnaires somewhere public and ask people to return their answers.

What is the strength of volunteer sampling?

Strength of volunteer sampling=

• 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 in the street

What are the weaknesses of the volunteer sampling?

Weaknesses of volunteer sampling=

• 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)

• Only people who see the advertisement have a chance of being selected – this affects the generalizability of the findings.