Introduction to a variety of useful statistical ideas and techniques - Improving the User Experience through Practical Data Analytics - page 1

CHAPTER

1

Introduction to a variety
of useful statistical ideas
and techniques

1.1 INTRODUCTION
In this introductory chapter, we present several basic statistical fundamentals that will
help get you ready for the techniques that begin in Chapter 2. If you're already familiar
with these fundamentals, you may prefer to skim this chapter or proceed directly to
Chapter 2. But we believe that it will be worth your time—even for the busiest UX
(User Experience) researcher—to spend a little time with the ideas in this chapter. We
have made a concerted effort to try to make this background material easily digestible.

1.2 THE GREAT NORMAL CURVE IN THE SKY
There are many phenomena in nature that are determined by the probabilities associ-
ated with a normal curve . The normal curve is also called the “bell-shaped curve,”
the “bell curve,” and by engineers, often, the “Gaussian curve.”
In fact, we can also explain a lot of unusual phenomena by what is inferred or pre-
dicted by a bell-shaped curve. Indeed, professors teaching statistics will often refer
to pure luck—the purposeless, unpredictable, and uncontrollable force that shapes
events favorably or unfavorably for an individual, group, or cause—as governed by
the “Great Normal Curve in the Sky.” We're so enamored with the normal curve that
we requested that one appear on the cover of this topic—and the good folks at Mor-
gan Kaufmann made it happen.
So, what is this normal or bell-shaped curve? When you construct a histogram with
a large number of data points (basically, a bah chart—oops, sorry, the Boston accent
crept in—a bar chart), the result, when smoothed out a bit, will be a normal curve if the
contour of the curve has a certain shape, indeed, referred to as a normal curve.
The normal curve is based on a complicated mathematical equation that we don't
really need to know and has a basis in the physics of our planet, Brownian motion,
and lots of other stuff that none of us may want to even think about. Well, at least not
right now. May be a picture is the best place to start to describe the normal curve. A
set of normal curves is pictured in Figure 1.1 .
The normal curve (and now you can see why it is also called the bell-shaped curve; it
looks like the outline of the Liberty Bell in Philadelphia) is really a family of curves. It can
center at any point, but that point is always its mean, median, and mode. The normal curve