Page 29 - Statistics II for Dummies

Chapter 1: Beyond Number Crunching: The Art and Science of Data Analysis 13

Funny thing, too. When Sue went on a late night TV program to show the
world her incredible horse, someone in the audience noticed that whenever
the horse got to the correct number of stomps, Sue would interrupt him and
say “Good job!” and the horse quit stomping. He didn’t know how to count;
all he knew to do was to quit stomping when she said “Good job!”
Redoing analyses in different ways in order to try to get the results you want
is called data fishing, and folks in the stats biz consider it to be a major no-no.
(However, people unfortunately do it all too often to verify their strongly held
beliefs.) By using the wrong data analysis for the sake of getting the results
you desire, you mislead your audience into thinking that your hypothesis is
actually correct when it may not be.

Getting the Big Picture:

An Overview of Stats II

Stats II is an extension of Stats I (introductory statistics), so the jargon fol-
lows suit and the techniques build on what you already know. In this section,
you get an introduction to the terminology you use in Stats II along with a
broad overview of the techniques that statisticians use to analyze data and
find the story behind it. (If you’re still unsure about some of the terms from
Stats I, you can consult your Stats I textbook or see my other book, Statistics
For Dummies (Wiley), for a complete rundown.)

Population parameter

A parameter is a number that summarizes the population, which is the entire
group you’re interested in investigating. Examples of parameters include the
mean of a population, the median of a population, or the proportion of the
population that falls into a certain category.

Suppose you want to determine the average length of a cellphone call among
teenagers (ages 13–18). You’re not interested in making any comparisons;
you just want to make a good guesstimate of the average time. So you want to
estimate a population parameter (such as the mean or average). The popu-
lation is all cellphone users between the ages of 13 and 18 years old. The
parameter is the average length of a phone call this population makes.

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