CHAPTER 24 Ten Distributions Worth Knowing 351

Chapter 24

Ten Distributions Worth

Knowing

T

his chapter describes ten statistical distribution functions you’ll probably

encounter in biological research. For each one, we provide a graph of what

that distribution looks like, as well as some useful or interesting facts and

formulas. You find two general types of distributions here:»

» ^{Distributions that describe random fluctuations in observed data: Your}

study data will often conform to one of the first seven common distributions.

In general, these distributions have one or two adjustable parameters that

allow them to fit the fluctuations in your observed data.»

» ^{Common test statistic distributions: The last three distributions don’t describe}

your observed data. Instead, they describe how a test statistic that is calculated

as part of a statistical significance test will fluctuate if the null hypothesis is true.

The Student t, chi-square, and Fisher F distributions allow you to calculate test

statistics to help you decide if observed differences between groups, associations

between variables, and other effects you want to test should be interpreted as

due to random fluctuations or not. If the apparent effects in your data are due

only to random fluctuations, then you will fail to reject the null hypothesis. These

distributions are used with the test statistics to obtain p values, which indicate

the statistical significance of the apparent effects. (See Chapter 3 for more

information on significance testing and p values.)

IN THIS CHAPTER»

» ^{Delving into distributions that may}

describe your data»

» ^{Digging into distributions that arise}

during statistical significance testing