4. Detect influential factors

The influence of a factor on a considered response is generally based on the estimation of the critical effect size ( ^{E _-} ) above which the effect of a factor should be considered significant. Wherever possible, a statistical approach derived from Student's T-test should be preferred (Y. Vander Heyden et al.). Beyond statistical analysis, the study's conclusions must also be examined in the light of critical thresholds defined by the analyst with regard to non-statistical criteria. Indeed, statistical significance is not necessarily synonymous with practical or technical relevance. For example, if a variation of ±0.02 mL/min in flow rate is shown to significantly affect the retention factor of an HPLC method, with an effect of amplitude 0.05 minutes compared to the normal response of 13 minutes, this may not be...