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Population
a whole set of items of interest
information obtained from a population
raw data
census
observes or measures every member of a population
sample
a selection of observations taken from a subset of the population, which is used to find out information about the whole population
advantages of doing a census
gives completely accurate results
disadvantages of doing a census
time-consuming and expensive
cannot be used when the testing process destroys the item
hard to process large quantities of data
advantaged of using samples
less time-consuming and expensive than a census
fewer people have to respond
less data to process than a census
disadvantage of using samples
data may not be representative of the whole population
samples may not be large enough to give information about small subgroups of the population
sample size can affect the validity of any conclusion drawn
sample size depends on required accuracy and available resources
larger samples are more accurate but require more resources
varied populations need larger samples than uniform populations
different samples can lead to different conclusions due to the natural variations in a population
individual units of a population
sampling units
sampling units of a population are often individually named or numbered to form a list called
sampling frame
