sampling Flashcards
what is the difference between a population and a sample?
population refers to the large group of individuals that a particular researcher is interested in studying, whereas a sample is the smaller subset of the target population that take part in the investigation
name the different sampling techniques
random, stratified, systematic, opportunity, volunteer, snowball and quota
define each sampling technique
random - when all members of the target population have an equal chance of being selected
systematic - using a predetermined system to select ppts
stratified - when subgroups of a population are identified and ppts are obtained from each group in proportion to their occurrence in the population
opportunity - recruiting those who are most convenient or most available
volunteer - gaining a sample through advertising
snowball - relies on referrals from initial ppts to generate additional ppts
quota - ppts are selected according to their frequency in the population
what is the difference between stratified and quota sampling?
with stratified sampling the selection is done randomly, whereas with quota sampling the selection is done using another method
strengths and weaknesses of random sampling
strengths - unbiased
weaknesses - difficult and time consuming, sample may still be unrepresentative and ppts may refuse to take part
strengths and weaknesses of systematic sampling
strengths - unbiased
weaknesses - not necessarily truly unbiased, time consuming and ppts may refuse to take part
strengths and weaknesses of stratified sampling (and quota sampling)
strengths - produces a representative sample and generalisation of findings becomes possible
weaknesses - complete representation is impossible and it is time consuming
strengths and weaknesses of opportunity sampling
strengths - convenient
weaknesses - suffers from population bias and researcher bias
strengths and weaknesses of volunteer sampling
strengths - easy, less time consuming, ppts are more engaged and it may be more representative
weaknesses - volunteer bias
strengths and weaknesses of snowball sampling
strengths - able to locate people who are difficult to access
weaknesses - not a good cross-section from the population as it is friends of friends
how would you carry out a random sample?
- obtaining a complete list of all members of the target population
- all names on the list are assigned a number
- the actual sample is selected using a lottery method
how would you carry out a systematic sample?
- producing a sampling frame (a list of people in the target population organised into something like alphabetical order)
- a sampling system is nominated
- the researcher works through the sampling frame until the sample is complete
how would you carry out a stratified sample?
- identifying the strata that make up the population
- the proportions needed for the sample to be representative are worked out
- the ppts that make up each stratum are selected using random sampling
