When carrying out the experiment, care has to be taken that other variables that affect the rate of reaction, such as concentration of reactants, are kept constant. These are control variables.

In mixture experiments with process variables, the response depends not only on the proportions of the mixture components, but also on the effects of the process variables. In many such ...

When carrying out the experiment, care has to be taken that other variables that affect the rate of reaction, such as concentration of reactants, are kept constant. These are control variables.