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We have many ways to describe a collection of data. We will explain and illustrate many such ways in this section.
There is a distinction that should be made at this point.
We distinguish between population and sample characteristics
by referring to population characteristics as population parameters
and sample characteristics as sample statistics.
Thus, the mean of a population is a parameter of that
population, but the mean of a sample is a statistic
of that sample.
Beyond that distinction
there is no difference in the naming or computing
for the
measures mode, the median,
the range, and the quartiles.
The mean of a population, μ, has
a different symbol from the one used for the mean of a sample,
,
however the computation of each is the same.
Standard deviation has both
different symbols, σ for a population
and sx for a sample, and
a slightly different formula. That difference will be illustrated in
the subsequent web page
measures of dispersion.