Used extensively in ANOVA and design of experiments, investigators select factors to systematically vary during an experiment in order to determine their effect on the response variable. Factors can only assume a limited number of possible values, known as factor levels. Factors can be a categorical variable or based on a continuous variable but only use a few controlled values in the experiment.
For example, you are studying factors that could affect plastic strength during the manufacturing process. You decide to include the following two factors in your experiment:
|
Factor |
Additive |
Temperature |
|
Level |
A |
Low (100C) |
|
Level |
B |
Medium (150C) |
|
Level |
|
High (200C) |
The additive is a categorical variable. It can only be type A or type B. On the other hand, temperature is a continuous variable, but here it is a factor because only three temperatures settings of 100C, 150C and 200C are tested in the experiment.