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Gravity
Terms in this set (22)
population
entire group of individuals or instances about whom we hope to learn (parameter)
sample
(statistic) a representative subset of a population. Hope to learn about the population
sample survery
study that asks questions of a sample drawn from some population in hopes of learning about the entire population. Example: polls
bias
a failure of a sampling method. over or underestimate parameters. Almost impossible to recover from bias.
randomization
each individual is given a fair, random chance of selection. best defense against bias
sample size
number of individuals in the sample
census
sample that consists of the entire population
population parameter
numerically valued attribute of a model for a population. Estimated from sampled data.
statistic, sample statistic
values calculated for sampled data. Estimate the population parameter
representative
if the statistics computed from the sample accurately reflects the corresponding population parameters
simple random sample
each set of n elements in the population has an equal chance of selection
sampling frame
list of individuals from whom the sample is drawn. Included in sample
stratified random sample
population is divided into several subpopulations (strata) and random samples are drawn from each stratum. homogeneous
cluster sample
sampling design in which entire groups (clusters) are chosen at random. Usually selected as a matter of convenience/practicality/cost. heterogeneous.
multistage sample
sampling schemes that combine several sampling methods.
systematic sampling
selecting individuals systematically from a sampling frame.
pilot study
small trial run of survey. check if questions are clear. reduce errors due to ambiguous questions.
voluntary response bias
bias introduced to a sample when individuals can choose whether or not to participate in the sample. always invalid. cannot be recovered.
convenience sample
individuals who are conveniently available. fail to be representative because not every individual is equally convenient.
undercoverage
gives part of the population less representation.
nonresponse bias
large fraction of those sampled fails to respond. those who respond do not represent the entire population. voluntary response.
response bias
anything in a survey design that influences responses. the wording of questions.
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