The order in which the independent variables are assigned to the vertical column is essential. In the case of mixed variables and interaction between variables, the variables are to be assigned at right columns as stipulated by the orthogonal array. Hence, TPC, TEVA and Temperature are assigned to columns 1,2 and 3 respectively as shown below in table 2.

Conducting the experiment

Randomisation is the mixing or shuffling of the order in which events occur so that each have an equal chance of being selected. There is a substantial amount of uncontrolled or residual variation in any experiment, so no test can ever be repeated exactly. This residual variation is caused by factors, which have not been (or cannot be) controlled by the experimenter. These factors are called uncontrolled factors. Randomisation reduces the effect of these uncontrollable factors. Failure to randomise can cause successive error terms to be correlated, which can lead to misleading data acquisition (Ranjit, Roy, 1996).

Now that the orthogonal array has been selected the experiments are conducted as per the level combinations. It is essential that all the experiments be conducted. The experiments are run in random order.