Introduction

Step-by-step analysis of biological data

Types of biological variables

Probability

Basic concepts of hypothesis testing

Confounding variables

Independence

Normality

Data transformations

See the
*Handbook* for information on these topics.

### Homoscedasticity and heteroscedasticity

Bartlett’s test is performed with the *bartlett.test*
function. Levene's test can be invoked with the *leveneTest* function in
the *car* package. This test can also be used for a model with two
independent variables. They are used in the chapter on *One-way anova*.