Page 146 - Statistics for Dummies

In this part . . .
tatisticians study populations; that’s their bread
Sand butter. They measure, count, or classify charac-
teristics of a population (using random variables); find
probabilities and proportions; and create (or estimate)
numerical summaries for the population (that is, param-
eters for the population). Sometimes you know a great deal
about a population from the start; sometimes it’s hazier.
This part studies populations under both scenarios.
If a population fits a specific distribution, tools are avail-
able for studying it. In Chapters 8 through 10, you see three
commonly used distributions: the binomial distribution
(for categorical data) and the normal and t-distributions
(for numerical data).
If the specifics about a population are unknown (as hap-
pens most of the time), you take a sample and generalize
its results to the population. However, sample results vary,
and you need to take that into account. In Chapter 11 you
investigate sample variability, measure the precision of
your sample results, and find probabilities for their likeli-
hood. From there you’ll be able to properly estimate
parameters and test claims made about them, but that’s
another Part — IV, to be exact.

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