chapter one - year one Flashcards
what is a census
observes or measures every member of a population
what is an advantage of a census
it should give a completely accurate result
what are the disadvantages of a census
- time consuming and expensive
- cannot be used when the testing process destroys the item
- hard to process large quantity of data
what is a sample
a selection of observations taken from a subset of a population which is used to find out information about the population as a whole
what are the advantages of a sample
less time consuming and expensive than a census
fewer people have to respond
less data to process than in a census
what are disadvantages of a sample
the data may not be as accurate
the sample may not be large enough to give information about small sub-groups of the population
what is simple random sampling
what every sample of size n had an equal chance of being selected
what are advantages of simple random sampling
free of bias
easy and cheap to implement for small populations and small samples
each sampling unit has a known and equal chance of selection
what are disadvantages of simple random sampling
not suitable when the population size or the sample size is large
a sampling frame is needed
what is systematic sampling
the required elements are chosen at regular intervals from an ordered list
what are advantages of systematic sampling
simple and quick to use
what are disadvantages of systematic sampling
a sampling frame is needed
it can introduce bias if the sampling frame is not random
what is stratified sampling
the population is divided into mutually exclusive strata and a random sample is taken from each
no. in stratum/no. in population x overall sample size
what are advantages of stratified sampling
sample accurately reflects the population structure
guarantees proportional representation of groups within a population
what are disadvantages of stratified sampling
population must be clearly classified into distinct strata
selection within each stratum suffers from the same disadvantages as simple random sampling: sampling frame needed and not suitable when the population size or the sample size is large
what is quota sampling
an interviewer or researcher selects a sample that reflects the characteristics of the whole population
what are advantages of quota sampling
allows a small sample to still be representative of the population
no sampling frame needed
quick, easy and inexpensive
allows for easy comparison between different groups within a population
what are disadvantages of quota sampling
non random sampling can introduce bias
population must be divided into groups, which can be costly or 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 ( convenience sampling )
consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for
what are advantages of opportunity sampling
easy to carry out
inexpensive
what are disadvantages of opportunity sampling
unlikely to provide a representative sample
highly dependent on individual researcher
