Sample Selection and Techniques Flashcards
what is a random sample ?
when every member of a target population has an equal chance of being selected
what are two positives of using a random sample ?
1) unbiased - all target population had an equal chance of being selected
2) possible to choose a subgroup in the target population first, which makes it easier to randomly elect ppts
what are three negatives of using a random sample ?
1) takes more time and effort than other techniques because you need to obtain a list of all the names in the target population, randomly pick and then contact them.
2) random samples are not often random because not all ppts will be willing to take part - sample may end up being more like a volunteer sample
3) if the sample is an independent groups design, it could be that one group ends up having a higher performance standard than the other (higher IQ or sporting capability)
what is a stratified sample ?
participants are selected from different subgroups (strata) in the target population in the proportion to the subgroups’s frequency in that population
what are two positives of using a stratified sample ?
1) most representative of all the sampling techniques because all the subgroups are included and represented in proportion to the numbers in the target population
2) specific subgroups can be chosen according to the variables considered to be important by the researcher - increases control over extraneous variables
what are two negatives of using a stratified sample ?
1) decision on what subgroups to use can be biased - reducing representativeness
2) method is a lengthy process and ppts selected may choose not to take part - means method not used in psychological research much (except when conducting opinion polls)
what is a volunteer sample ?
a sample of ppts produced by asking for people willing to take part.
what are two positives of using a volunteer sample ?
1) convenient way to get sample of willing ppts - committed ppts are less likely to drop-out
2) may be good to get specialised group of ppts - this is purposive sampling (e.g., if you wanted to study the behaviour of medical students, it would make sense to advertise the study on the noticeboard of a medical school)
what are two negatives of using a volunteer sample ?
1) sample can be biased because volunteer ppts are likely to be more motivated and/or have more time on their hands than the general population
2) volunteers may also be more willing to be helpful and thus may be more prone guessing the aims of the study and respond to demand characteristics
what is an opportunity sample ?
a sample of ppts produced by selecting people who are most easily available at the time of the study. (e.g., asking people walking by you on the street)
what are two positives of using an opportunity sample ?
1) more convenient technique because it takes little preparation (you are asking the most available people)
2) may be the only technique available if the whole target population cannot be listed (which is needed for random and stratified)
what are two negatives of using an opportunity sample ?
1) inevitably biased - sample is drawn from small part of the target population (not likely to representative)
2) ppts may refuse to take part so the final sample also has the weakness of a volunteer sample (only eager people take part and so are more likely to respond to demand characteristics)
