Sampling Flashcards
what is sampling?
1
the method used to select participants to take part in the study
sample taken should represent…
3
the type of people in the target population, which is the group of people the researcher is interested in generalising their findings to
e.g. people in the UK, young people living in london
allows generalisations about the population to be made
5 types of sampling
5
opportunity
volunteer
stratified
systematic
random
what is opportunity sampling?
2
use whoever is immediately available, most convenient and willing to take part at the time of the study
e.g. people in your school or passers by on the street
advantages of opportunity sampling
2
easiest way to get participants, just use first suitable people you find so you don’t spend as much time locating your sample
therefore saves time and money
disadvantages of opportunity sampling
3
inevitably bias and harder to generalise as it only has participants from a specific and small part of the population
sample may also be bias as researcher may have chosen a specific area to prove their point
e.g. if you select your sample from people in town in a monday morning then it would be unlikely to include professional people because they’d be working and unlikely to include people from rural areas because they live further away
what is random sampling?
2
every member of the target population has an equal chance of being selected
selected randomly using a computer generator
advantages of random sampling
1
least likely to have sample bias as all members of the sample have an equal chance of selection
disadvantages of random sampling
2
time consuming — need to have a list of all the members of the population and then contact everyone selected, asking if they wish to take part
a lot of people may decline to take part, which means that building a sufficient sample takes even more time
what is stratified sampling?
3
identify subgroups within a population (age groups, gender, etc)
participants are obtained from each group in proportion to their occurrence in the population
selection from each subgroup is done randomly
advantages of stratified sampling
2
likely to be much more representative of the target population due to proportional representation of subgroups
therefore more easy to generalise to the target population
disadvantages of stratified sampling
2
more time consuming as you have to identify subgroups, randomly select participants and contact them
many might decline to take part, meaning you have to keep asking until you have enough participants
what is systematic sampling?
3
participants are selected systematically from the population
selecting every nth person from the list, usually starting at a random number — e.g. every 6th person on the list is selected, starting at the 8th name down and this numerical interval is applied consistently
may select such names from a phonebook
advantages of systematic sampling
1
unbiased as participants are selected using an objective system
disadvantages of systematic sampling
2
more time consuming
not truly unbiased or random unless you select a number using a random method and start at that number, selecting every nth person
what is volunteer sampling?
2
use whoever puts themselves forward through an advertisement in a newspaper, notice board or on the internet
relies solely on people volunteering to be a part of the sample
advantages of volunteer sampling
2
less likely to drop out as they’ve signed up for it and know what they have to do, people who volunteer are likely to be more highly motivated and enthusiastic about taking part
gives access to a variety of participants, for example everyone who reads a certain newspaper, especially true if you’ve advertised on more than one platform, may lead the sample to be more representative and less biased
disadvantages of volunteer sampling
2
increased demand characteristics as they’re more motivated and enthusiastic about taking part, they might try to be helpful or appear a certain way so change their behaviour — demonstrates that the sample is biased in other ways, mainly volunteer bias
might not be representative of the population as the method of advertisement may only attract a certain type of person e.g. advertising on the internet may only attract younger people
what is bias?
4
a systematic distortion
EXAMPLES = experimenter bias, interviewer bias, observer bias, social desirability bias, sample bias, volunteer bias
sample bias describes a sample that is inevitably biased or distorted because it is not truly representative of the population
volunteer bias describes the idea that people who volunteer are likely to be different to other members of the population, they may be more highly motivated for example, this distorts or biases the data they produce as they may not be representative of the population
what is generalisation?
1
applying the findings of a particular study to the population that the researcher is interested in
what is volunteer bias?
3
a form of sampling bias
volunteer participants have special characteristics — they tend to be more highly motivated than randomly selected participants
alternatively, they may be quite financially insecure so need the money offered for participation
random techniques used in random sample
2
THE LOTTERY METHOD — obtain a list of all the people in the population, put all these names in a hat, draw the number of names required out of the hat, use these as participants
RANDOM NUMBER GENERATOR — number every member of the population, may use a computer programme such as microsoft excel to type =RAND(100) to get a random number between 1 and 100, repeat this until you’ve selected enough people for your sample
