Statistical Analysis with R Essentials For Dummies

Chapter 7

What’s Normal?

IN THIS CHAPTER

Meeting the normal distribution family

Working with standard deviations and the normal distribution

Understanding R’s normal distribution functions

One of the main jobs of a statistician is to estimate characteristics of a population. The job becomes easier if the statistician can make some assumptions about the populations he or she studies.

Here’s an assumption that works over and over again: A specific attribute, ability, or trait is distributed throughout a population so that (1) most people have an average or near-average amount of the attribute, and (2) progressively fewer people have increasingly extreme amounts of the attribute. In this chapter, I discuss this assumption and its implications for statistics. I also discuss R functions related to this assumption.

Hitting the Curve

It’s possible to capture this assumption in a graphical way. Figure 7-1 shows the well-known bell curve that describes the distribution of a wide variety of attributes. The horizontal axis represents measurements of the ability under consideration. A vertical line drawn down the center of the curve would correspond to the average of the measurements.