Applied maths chapter 1

what is a population

the whole set of items that are of interest

what is a census

something that observes or measures every member of a population

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

advantages of a census

should give a completely accurate result

disadvantages of a census

time consuming and expensive

cannot be used when the testing process is destructive

hard to process large quantities of data

sample advantages

less time consuming and expensive

fewer people need to respond

less data to process

sample disadvantages

data may not be a s accurate

sample may not be large enough to give info about small sub groups of the populationj

individual units of a population are known as

sampling units - often individually named or numbered

what are the three methods of random sampling

simple random

systematic

stratified

in stratified sampling, the strata must be…

mutually exclusive

advantages of simple random sampling

free of bias

easy and cheap for small populations and samples

each sampling unit has a known and equal chance of selection

disadvantages of simple random sampling

not suitable when population/sample size is large as it is potentially time consuming, disruptive and expensive

sampling frame needed

systematic sampling advantages

simple and quick

suitable for large samples and populations

systematic sampling disadvantages

sampling frame needed

can introduce bias if sampling frame is not random

stratified sampling advantages

sample accurately reflects population structure

guarantees proportional representation of groups within a population

stratified sampling disadvantages

population must be clearly classified into distinct strata

selection within each stratum has the same disadvantages as simple random sampling

what is quota sampling

when the sample is chosen to reflect the characteristics of the whole population

opportunity sampling is

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

quota sampling advantages

small sample can still be representative

no sampling frame required

quick easy and cheap

allows for easy comparison between different groups in a population

disadvantages of quota sampling

non random so can be biased

population must be divided into groups - costly/inaccurate

increasing scope of study increases number of groups - time and expense

non-responses not recorded as such

opportunity sampling advantages

easy and cheap

opportunity sampling disadvantages

unlikely to be representative

highly dependent on individual researcher