sampling Flashcards
what is a target population
every member of the group the investigator plans to study.
why can’t the whole target population be studied
they could contain millions of people
who do researchers conduct their experiments on
a smaller sample of participants taken from the larger target population. the results/behaviour of that sample are assumed to apply to all members of the target population
what is generalisation
the application of the results from a study, to the wider target population.
what does the generalisability of results depend on
how representative the sample is of the target population meaning the sample used in the study shares characteristics with the members of the target population (e.g. gender, ethnicity, age, education level, income level)
what is random sampling
each member of the target population has a mathematically equal chance of being in the experimenters sample
what is the procedure of random sampling
1) researchers need a full list of the entire target population
2) all names entered into a container (computer database)
3) a number of games equal to the sample required are pulled from the container (the computer is instructed to randomly select the names)
4) the names are selected from the sample
what are the strengths of random sampling
a random sample avoids researcher bias as the researcher can not 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.
what are the weaknesses of random sampling
by chance, participants could be pciked that produce an unrepresentative sample. for e.g two 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
what is systematic sampling
participants are chosen from a list of the target population. every nth participant is chosen to form the sample (e.g. every 5th, 10th or 100th name)
what is the procedure of systematic sampling
1) the researcher needs a full list of the entire target population
2) the researcher reads down the list selecting every nth participant to form the sample
3) the process continues until the sample required is chosen
what are the strengths of systematic sampling
it 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 (student registers) it can be a quick method of selecting a sample
what are the weaknesses 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
what is opportunity sampling
the researcher directly asks available members of the target population to take part in the research. its likely to be individuals the researcher has easy access to and is familiar with
what is the procedure of opportunity sampling
1) researcher directly asks any members from within the target population (that they have access to) to take part in the research
2) any individuals who agree to take part are added to the sample until the number of participants required is met
what are the strengths 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.
what are the weaknesses of opportunity sampling
as the researcher decides who to ask and who not to ask to take part this could result in researcher bias meaning the researcher may select participants they are feel are likely to produce a preferred result.
it is unlikely to be representative as the participants chosen are the type of people the researcher has easy access to. for e.g. for research conducted in universities, its likely to be young undergraduate students
what is volunteer sampling
also known as a self selecting sample. participants offer to take part after finding out about the research. not directly asked by the researcher. likely after seeing an advert or newspaper online
what are the procedures for volunteer sampling
1) advertisements are placed where they are likely to be seen by members of the target population (e.g. the gym for fitness enthusiasts, the pub for alcoholics)
2) the advert will include details and the researcher will enrol the volunteer into the sample when they are contacted by the volunteer
what are the strengths of volunteer sampling
advertising for participants can reach a very large number of potential participants, especially if the newspaper or website is widely read
an easy sample to collect as participants are putting themselves forward rather than having to be found individually and contacted directly
what are the weaknesses of volunteer sampling
the sample may not be generalisable to the target population because of volunteer bias. the types of people who volunteer to take part are likely to have different characteristics to the target population, they are likely to be friendlier and have more free time available
what is stratified sampling
by selecting participants within strata, the characteristics of participants within the sample are in the same proportion as found within the target population
what is the procedure for stratified sampling
1) strata/subgroups are identified along with their proportion in the target population (e.g. gender, ethnicity, education level)
2) random sampling is then used to select the number of participants required from within each stratum
what are the strengths of stratified sampling
- the sample is representative of the larger target population meaning the results found within the sample should be generalisable to the target population
- as the participants are randomly chosen from within each stratum, this avoids researcher bias
what are the weaknesses 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 strata
