advantage of a census
it should give a completley accurate result
disadvantages of a census
- time consuming
- cannot be used when the testing process destroys the item
- hard to process large quantity data
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
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
define census
observers of measures every member of a population
define sample
a selection of observations taken from a subset
what are sampling units
individual units of a population
what is a sampling frame
often sampling units of a population are individually named or numbered to form a list
what are the three methods of random sampling
1.simple random
2. systematic
3. stratified
what is simple random sampling
where every sample of size n has an equal chance of being selected
what is systematic random sampling
the required elements are chosen at regular intervals from an ordered list
what is stratified sampling
the population is divided into mutually exclusive strata (males and females, for example) and a random sample is taken from each
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
disadvantages of simple random sampling
- not suitable when the population size or the sample size is large as it is potentially time consuming, disruptive and expensive
advantages of systematic sampling
- simple and quick to use
- suitable for large samples and large populations
disadvantages of systematic sampling
- a sampling frame is needed
- it can introduce bias if the sampling is not random
advantages of stratified sampling
- sample accurately reflects the population and structure
- guarantees proportional representation of groups with a population
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
2 examples of non-random sampling
- quota
- opportunity
what is quota sampling
an interviewer or researcher selects a sample that reflects the characteristics of the whole population
advantages of quota sampling
- allows a small sample to still be representative of the population
- no sampling frame required
- quick, easy and inexpensive
- allows for easy comparison between different groups within a population
disadvantages of quota sampling
- non-random sampling can introduce a 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 recorded as such
what is opportunity sampling
- consits 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
advantages of opportunity sampling
- easy to carry out
- inexpensive
