stats Flashcards
(16 cards)
what is the definition of a population?
a whole se of individuals/individual items of interest
what is a sampling frame?
a list of items
what is simple random sampling
NEEDS A SAMPLING FRAME, each person or thing fron the sf is then allocated a unique number and a selection of these numbers is chosen at random e.g by random number generator or lottery
advantages of simple random sampling
free of bias
easy and cheap to implement for small samples/populations
each sampling unit has a known and equal chance of selection
disadvantages of srs
not suitable when the population size or the sample size is large as it is potentially time consuming and expensive
sampling frame is needed
what is stratified sampling
where the population is divided into mutually exclusive strata and a random sample is taken from each strata
no sampled in stratum = (no in strata / no in population) x overall sample size
advantages of stratified sampling
sample accurately reflects population structure
guarantees proportional representation across groups within a population
disadvantages of strat sampling
populations must be clearly classified into distinct strata
selection within each stratum suffers from the same disadvantages as srs
what is systematic sampling
where a number is chosen at random to start the sample, and then further numbers are chosen in regular increments.
e.g you want to systematically sample 20 pieces of data and extract 5 data. use a random number generator to choose from 1-4. after this go up in increments of 4
what is quota sampling
where an interviewer selects a sample that reflects the characteristics of the whole population - NOT RANDOM.
the interviewer would:
meet people
assess their group
after interview allocated them into an appropriate quota
once the quota is full no more responses can be taken, move onto the next quota or finish
advantages of quota sampling
allows a small sample to still be representative of the population
no sampling frame required
quick easy inexpensive
allows for easy comparison between different groups in a population
disadvantages of quota sampling
non random sampling can introduce bias
population must be divided into groups which can be costly and inaccurate
increasing scope of study increases number of groups which adds time and expense
non responses are not recorded as such
what is opportunity sampling
asking the first x amount of people for their responses
what are the advantages to opportunity sampling
easy to carry out
inexpensive
disadvantages of opportunity sampling
unlikely to provide a representative sample
highly dependent on individual researcher
what is a census
an observation/study of every member of a population
