Data collection

Census

measures every member of a population

census advantages

provides completely accurate result

census disadvantages:

time consuming

expensive

cannot be used when testing breaks item

hard to process large amounts of data

Sample definition

measures a subset of the population to work out infromation of the whole population

sample advantages:

less time consuming

fewer people have to respond

less data to process

sample disadvantages:

data may not be fully accurate

sample may not be large enough to give accurate enough data.

Simple random sampling

small groups are selected from a larger group in a way that each member of the population has an exactly equal chance of being picked

simple random sampling advantages

not suitable when the population size is overly large, sampling frame required

systematic sampling

the required elements are chose at regular intervals from an ordered list

systematic sampling advantages

simple and quick to use, suitable for large samples and large populations

systematic sampling disadvantages

sampling frame needed which can introduce bias if sampling not randoms

stratified sampling

the population is divided into mutually exclusive strata

stratified sampling advantages

sample accurately reflects the population sturcture, guarantees proportional representation of groups withitn a population

stratified sampling disadvantages

population must be clearly classified into distinct strata

quota sampling

an interviewer or researcher selects a sample that reflects the characteisitics of the whole populationad

quota sampling advantages

allows a small sample to still be representative of the population, no sampling frame, quick, easy, cheap and allows easy comparisondis

quota sampling disadvantages

Non random can introduce bias, populations must be divided into groups, increasign scope of study adds time and expenses.

Opportunity sampling

taking a sample from people who are available at the time of study

Opportunity sampling advantages

easy to carry out, inexpensive

Opportunity sampling disadvantages

unlikely to provide a representative sample, highly dependent on individual researchers.