sampling Flashcards
What is a target population?
The large group of people that a researcher is interested in studying e.g. college students from the north west
What is a sample?
It is usually to include all members of the population in the study, so a smaller group is selected
What is a random sample?
All members of the target population have an equal chance of being selected
How do you select a random sample?
- a complete list of all members of the target population is obtained, all names assigned a number, generated through use of lottery method e.g. picking numbers from a hat
Strength of random sampling
- free from researcher bias, no influence over who is selected
- equal chance of selection, most representative sample in which we can generalise findings to target population
Weakness of random sampling
- difficult and time-consuming to conduct, complete list of target population difficult to obtain
- time consuming and costly opportunity sample more practical
Another strength of random sampling
- may end up sample that is still unrepresentative
- possible for random method to select e.g. 20 female psychology teachers from the north west
- reduces our ability to fully generalise findings
What is a systematic sample?
When every nth number of the target population is selected. For example very third house on the street
How to select a systematic sample
- sampling frame produced (list of people in target population organised into e.g. alphabetical order)
- sampling system nominates every nth person
- works through sampling frame until sample complete
Strength of systematic sample
- avoids researcher bias, no influence over who is chosen
- representative sampling method
Another strength of systematic sampling
- fairly representative sampling method, we should be able to generalise the results
Weakness of systematic sample
- selected participants may refuse to take part, which means you end up with something more like a volunteer sample. Response bias could be an issue
- this method could lead to an unrepresentative sample, reducing our ability to generalise the results to the target population
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 within the target population of the wider population
How to carry out a stratified sample
Researcher first identifies different strata that make up the population. Then, the proportions needed for the sample to be representative is worked out. Finally, the participants that make up each strata are selected using random sampling
Strength of stratified sampling
- avoids researcher bias, participants are randomly selected once divided into strata
- we should be able to generalise the results to the target population
weakness of stratified sampling
- identified strata cannot reflect all the ways that people are different, so complete representation of the target population is not possible
- this reduces our ability to generalise the results to the target population
another weakness of stratified sampling
- selected participants may refuse to take part, may end up something more like a volunteer sample
- this reduces our ability to generalise the results to the target population
What is an opportunity sample?
An opportunity sample is when researchers use participants who are readily available at the time of their research
How do you carry out an opportunity sample?
Ask whoever is around at the time of the study, for example in the street
Strength of opportunity sample
- quick and convenient method, uses readily available people at the time
- saves researcher time and effort and is much less costly
Weakness of opportunity sample
- suffer from two forms of bias
- sample is unrepresentative of the target population as it is drawn from a very specific area so cannot be generalised
- researcher has control over the selection of participants, this is called researcher bias
- this reduces our ability to generalise the results
What is a volunteer sample
Involves participants selecting themselves to be part of the sample, also referred to as a self-selection sample
How to select a volunteer sample
May place advert in a newspaper or on a notice board. Alternatively, willing participants may simply raise their hand when the research asks
Strength of volunteer sample
- easy to collect, requires minimal input from the researcher
- less time consuming and more cost effective than other forms of sampling
Weakness of volunteer sample
- volunteer bias is a problem, may attract a certain profile person who is keen, helpful and curious
- reduces the representativeness of the sample and reduces our ability to generalise the results to the target population
