Page 173 - Statistics for Dummies

Chapter 10
The t-Distribution
In This Chapter
▶ Characteristics of the t-distribution
▶ Relationship between Z- and t-distributions
▶ Understanding and using the t-table
he t-distribution is one of the mainstays of data analysis. You may have
Theard of the “t-test” for example, which is often used to compare two
groups in medical studies and scientific experiments.
This short chapter covers the basic characteristics and uses of the t-distribution.
You find out how it compares to the normal distribution (more on that in
Chapter 9) and how to use the t-table to find probabilities and percentiles.
Basics of the t-Distribution

In this section, you get an overview of the t-distribution, its main characteristics,
when it’s used, and how it’s related to the Z-distribution (see Chapter 9).

Comparing the t- and Z-distributions

The normal distribution is that well-known bell-shaped distribution whose mean
is μ and whose standard deviation is σ (see Chapter 9 for more on the normal
distribution). The most common normal distribution is the standard normal
(also called the Z-distribution), whose mean is 0 and standard deviation is 1.

The t-distribution can be thought of as a cousin of the standard normal
distribution — it looks similar in that it’s centered at zero and has a basic
bell-shape, but it’s shorter and flatter than the Z-distribution. Its standard
deviation is proportionally larger compared to the Z, which is why you see
the fatter tails on each side.

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