Sampling (Paper 2) Flashcards
(28 cards)
What is meant by the target population
Every member of the group that the investigator plans to study.
Can the entire target population always be studied
No, the target population could contain millions of people, so they can not all be studied.
Since the entire target population can’t be studied, what do researchers do
conduct their experiments on a smaller sample of participants, taken from the larger target population.
What is done with the results obtained from the sample of the target population
results/behaviour of that sample are generalised to all the members of the target population, this is generalisation.
What effects how accurately the results are generalised to the target population
How representative the sample is of the target population.
How can you tell how representative the sample is
Ask yourself if the sample used in the study shares characteristics with the members of the target population. (e.g. gender, ethnicity, age, education level, income level)
How does random sampling work
Each member of the target population has a mathematically equal chance of being in the experiment’s sample.
How can you conduct random sampling
Put all the names of the target population into a hat and pull the number of names out that you need in the sample
Give a strength of random sampling
A random sample avoids researcher bias as the researcher cannot choose the participants they want to form the sample, avoiding the possibility the researcher picks participants they feel are likely to give a preferred result.
Give a weakness of random sampling
By chance participants could be picked that produce an unrepresentative sample. For example too few members of one gender or with no members of a minority group.
It can be difficult and time-consuming to get a full list of a large target population.
How does systematic sampling work
Everynth person is chosen from a list
How do you conduct systematic sampling
The researcher needs a full list of the entire target population.
The researcher reads down the list selecting every Nth participant to form the sample (this can be any number for example every 5th, or 10th or 100th name)
The process continues until the sample required is chosen.
Give a strength of systematic sampling
Avoids researcher bias as the researcher cannot choose the participants they want in their sample.
If there is an existing list of the target population (e.g. student registers of a school/college ) it can be a quick method of selecting a sample.
Give a weakness of systematic sampling
By chance this method could result in an unrepresentative sample. E.g. too few members of one gender or with no members of a minority group.
If the target population is very large getting a full list could be difficult.
How does stratified sampling work
The proportions of people in population subgroups (strata) are reflected in the sample
How do you conduct a stratified sampling
Strata/subgroups are identified along with their proportion in the target population (e.g. gender, ethnicity, education level).
Random sampling is then used to select the number of participants required from within each stratum.
(e.g. 10% graduates and 90% non-graduates in the target population would result in 1 graduate and 9 non-graduates in a sample of 10)
Give a strength of stratified sampling
The sample is representative of the larger target population, meaning the results found with the sample should be generalisable to the target population.
As the participants are randomly chosen from within each stratum this avoids researcher bias.
Give a weakness of stratified sampling
Not every possible characteristic can be included in a stratified sample, and as the researcher decides which strata are important, this may result in bias.
Time-consuming to establish strata and then randomly select from each stratum
How does opportunity sampling work
Whoever is available at the time of sampling will be included
How do you conduct opportunity sampling
Researcher directly asks any members from within the target population to take part in the research
Any individuals who agree to take part are added to the sample until the number of participants required is met.
Give a strength of opportunity sampling
This is the fastest way to get a sample for psychological research, reducing the time it takes to conduct research and likely reducing the cost involved compared to more complex sampling methods.
Give a weakness of opportunity sampling
Opportunity samples are unlikely to be representative, as the participants chosen are the type of people the researcher has easy access to. For research conducted in universities, this is likely to be young undergraduate students.
How does volunteer sampling work
Participants ‘self - select’
How can you conduct volunteer sampling
Advertisements are placed where they are likely to be seen by members of the target population.
The advert will include contact details and the researcher will enrol the volunteer into the sample when they are contacted by the volunteer.
