research methods: sampling methods Flashcards
how are participants selected?
by sampling. it is very unlikely that the whole population can be used in the research so a sample of the population is gathered using a sampling technique.
what is the aim of sampling methods? and what problems could occur?
- aim of sampling methods is to ensure a representative sample of ppts is used; sample represents the characteristics of population well, so that any conclusions that are drawn from research can be successfully generalised to explain behaviour of target population as a whole
- if sample is gathered that is not representative due to over population or under representation of particular type of ppt then sampling bias can be issue
what is meant by target population? give example
refers to people study is about, people which findings can be applied to
e.g. study to investigate attitudes about nhs at local hospital, target population will be people at hospital. sample will be recruited from this target population using sampling technique
what are the four sampling techniques?
opportunity, random, stratified, volunteer/self-selected
what is opportunity sampling?
- opportunity sampling is the sampling technique most used by psychology students
- consists of taking the sample from people who are available at the time the study is carried out and fit the criteria you are looking for
strengths of opportunity sampling
- tends to be more ethical as researcher can judge, if ppt is likely to be upset by study or too busy to take part. other forms of sampling often do not give this information readily
- researcher has more control over who is asked, so finding ppts should be quick and efficient, because access is not a problem
weaknesses of opportunity sampling
- there is more chance of bias than with other methods. one source of bias is that researchers have more control over who is chosen and may be biased towards people who are easy to access, e.g. people they know. they may be more biased in choosing people like themselves, people of their own age or people who look friendly. this is likely to lead to a biased sample
- those who are picked are available and willing to take part in study, so they are self-selected. this would cause bias. these issues connected with ppts are likely to lead to biased sample.
what is random sampling?
- sampling technique defined as sample in which every member of population has equal chance of being chosen
- involves identifying everyone in target population and then selecting number of ppts you need in a way that gives everyone in population equal chance of being picked
strengths of random sampling
- no bias in the way ppts are chosen: everyone has opportunity to be chosen from sample. therefore, sample is likely to be representative of target population
- clear to everyone how sample was chosen. each step of process can be explained and understood. when studies are carried scientifically, their results and conclusions are more widely recognised and can be added more easily to body of psychological knowledge. with random sampling, any possible bias can be worked out mathematically and taken into account
weaknesses of random sampling
-difficult to ensure everyone in target population/sampling frame is available to be included on sample, which could cause bias. e.g. getting names of people because of Data Protection ACT 1998. even if everyone’s name was included, it would not be known if they were available to take part e.g. someone might not be available on required day or time specified
- when everyone has equal chance of being chosen, there can be bias in sample. e.g. if you wanted to investigate obedience in male and female soldiers, random sampling could potentially not select any female soldiers, which would not be useful
what is stratified sampling?
- involves classifying population into categories and then choosing sample which consists of ppts from each category in same proportion as they are in population. e.g target population is 60% female and 40% male, so sample is 60% female and 40% male
strengths of stratified sampling
- each group is bound to be represented, conclusions about differences between those groups can be made
weaknesses of stratified sampling
- groups set by study may not be important groups. having groups already decided means that some people will be **ruled out as ppts*. could mean that sample is not representative of population
- difficult to know how many of each group to choose in order to make sure findings are generalisable. always difficult to know how many individuals make up appropriate sample with stratified sampling, where numbers in each group may be small, it is harder
- efficient way to ensure there is representation from each group. limits numbers needed to obtain representation from each group
what is volunteer sampling?
- self selected sampling consists of ppts becoming part of study because they volunteer when asked or in response to advert
strengths of volunteer sampling
- more ethical than other methods as ppts come to researcher, rather than researcher seeking them out
- volunteers interested and perhaps less likely to give biased information or to go against researcher’s instructions. likely to be social desirability or demand characteristics - unless they are so keen that they do what they think the researcher wants having guessed what it is (demand characteristics). in general it is an advantage to have volunteers as they are willing to participate
