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mean, proportion, and variance are
unbiased estimators
List possible samples and find means.
The # of books sold over course of 4 day book fair were 139, 199, 241, 61. Assume sample size of 2
randomly selected w/replacement
Samples: 139139, 139199, 139241, 13961, 199139, 199199, 199241, 19961, 241139, 241199,
241241, 24161, 61139, 61199, 61241, 6161
Means: 139, 169, 190, 100, 169, 199, 220, 130, 190, 220, 241, 151, 100, 130, 151, 61
a
point estimate
is a single value used to approximate a population parameter. The sample mean x bar is
the best point estimate of µ because 1) for many populations, the distribution of sample means has less
variation than other measures of central tendency, and 2) sample means tend to center about the
population mean, not to systematically overestimate or underestimate µ
in the formula E=
zα2∙σn
you can replace σ with s if provided that n>30. If n ≤30 the population must
be normal and σ must be used in the formula
to determine whether to use the z or t distribution in computing the margin of error, E=
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 Fall '08
 Sapko
 Statistics, Variance

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