In the ANOVA models can contain fixed and/or random factors. For a **fixed **(**effect**)** factors**, we are interested in studying the specific levels in that factor. For a **random **(**effect**)** factor** data is collected for a random sample of possible levels, with the hope that these levels are representative of all levels in that factor. This approach can be appropriate where there are a large number of possible levels.

Models that contain both fixed and random factors are called **mixed models**. We will also consider **nested models** where one factor is lower in the hierarchy compared to another factor.

Topics: