Factor levels are the number of conditions, or levels, that a given factor will be run in the experiment. An example of a factor to be run at two levels is when the factor temperature is set at either 60 deg or 85 deg for the runs in an experiment. Nonlinear designs , and Response Surface Analysis, require more than 2 levels.
The levels for quantitative factors are usually based on the experimental range and on a need to evaluate these nonlinear effects. Those forqualitative factors are usually set by the categories inherent in the experiment (for example, Supplier A and Supplier B).
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