3.2 Sampling Design
population
 the entire group of individuals we want information about
sample
 the part of the population that we actually examine in order to gather information
sample survey
 survey a sample to gain info about the population
voluntary response sample
 consists of people who choose themselves by responding to a
general appeal
(EX online polls)
Voluntary response samples are biased because people with strong opinions, especially
negative opinions, are most likely to respond.
solution randomly select a sample
simple random sample (SRS)
 SRS of size n consists of n individuals from the population
chosen in such a way that every set of n individuals has an equal chance to be the sample
actually selected
label all individuals in population use software (or table of random digits) to select
sample of the desired size
•SRS gives each individual an equal chance to be chosen
•SRS gives every possible sample of size n an equal chance to be chosen
systematic random sample
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 Spring '08
 ABDUS,S.
 #, 6%, 4%, equal chance, •telephone survey

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