In this section, permeate flux data for each level of salt concentration, using the three different membranes, were tested using the standard F-test, Tukey's test, Fisher's LSD test, and finally Bonferroni's confidence interval test. Membrane type, therefore, is treated as a qualitative factor at three levels, as shown in Table 4. Therefore, μ1, μ2, and μ3 refer to the mean permeate flux using TF-200 (treatment 1), TF-450 (treatment 2), and TF-1000 (treatment 3). The effect of the variance of the measured data, as well as the level of type-I error (the so-called α value) are also investigated as they represent important factors in the decision-making process related to the choice of process variables and membrane type.