Sampling Flashcards
Why are samples used?
To make sure that our sample is representative of different groups within our population. This will make the sample represent the whole population, if it doesn’t the investigation may be biased.
Define the term random sampling.
Is a sophisticated form of sampling where all members of the target population have an equal chance of being selected.
- Obtain a list of all members of the target population.
- All of the names on the list are assigned a number.
- Actual sample is selected through the use of some lottery method (a computer/ phone randomiser or picking number a hat).
What are the strengths of random sampling?
Unbiased - meaning confounding or extraneous variables should be equally divided between different groups, enhancing internal validity.
What are the limitations of random sampling?
Is difficult and time-consuming to conduct.
Complete list of target population might be difficult to obtain.
May end up with a sample that’s still unrepresentative.
Selected participants may refuse to take part - ending up with something like a volunteer sample.
Define the term systematic sample.
Is when every nth member of the target population is selected.
A sampling frame is produced - list of people in the target population organisation into, eg alphabetical order.
A sampling method is nominated (every 3rd, 6th or 8th person, etc.
May begin from a random sample to reduce bias.
The researcher then works through the sampling frame until sample is done.
What are the strengths of systematic sample?
Objective - once system for selection has been established the researcher has no influence over who’s chosen.
What are the limitations of systematic sample?
Time-consuming.
Participants may refuse to take part, resulting in volunteer sample.
Define the term stratified sample.
Is a form of sampling when the composition of the sample reflects the proportions of people in certain subgroups (strata) within the target population or the wider population.
- Researcher identifies the different strata that make up the population.
- Proportions needed for the sample to be representative are worked.
- Participants that make up each stratum are selected using random sampling.
What are the strengths of stratified sample?
Produces a representative sample because it’s designed to accurately reflect the composition of the population - generalisation of findings becomes possible.
What are the limitations of stratified sample?
Can’t reflect all the ways that people are different - complete representation of target population isn’t possible.
Define the term opportunity sample.
When the researcher takes the chance to ask whoever is around at the time of their study, for example on the street.
What are the strengths of opportunity sample?
Less costly and time consuming.
What are the limitations of opportunity sample?
Unrepresentative of the target population as it draws from a specific area - findings can’t be generalised to target population.
Researcher has complete control over the selection of participants - may avoid people they don’t like the look of (researcher bias).
Define the term volunteer sample.
Involves participants selecting themselves to be part of the sample.
To select a volunteer sample researcher may place an advert in a newspaper or on a common room noticeboard.
What are the strengths of volunteer sample?
Collecting a volunteer sample is easy. Requires minimal input from the researcher and so less time-consuming .
Researcher ends up with people more engaged than someone stopped on the streets.
