Constructing confidence intervals to estimate a population
mean
Submitted by gfj100 on Wed, 11/11/2009  12:50
Previously we considered confidence intervals for 1proportion and our multiplier in our interval
used a zvalue. But what if our variable of interest is a quantitative variable (e.g. GPA, Age,
Height) and we want to estimate the population mean? In such a situation proportion confidence
intervals are not appropriate since our interest is in a
mean
amount and not a proportion.
Therefore we apply similar techniques but now we are interested in estimating the population
mean, μ, by using the sample statistic
and the multiplier is a tvalue. These tvalues come from
a tdistribution which is similar to the standard normal distribution from which the zvalues
came. The similarities are that the distribution is symmetrical and centered on 0. The difference
is that when using a ttable we need to consider a new feature:
degrees of freedom
(
df
). This
degree of freedom will be based on the sample size, n.
Initially we will consider confidence intervals for means of two situations:
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 Spring '11
 AndyRegards
 Statistics, Normal Distribution, 6.47 hours, 6.72 hours

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