2.3 Analysis of variance (ANOVA) and Scheirer-Ray-Hare
Grubb’s tests and normality tests (Shapiro-Wilk) were performed in Origin to identify and discard outliers (OriginPro, Version 2018G, OriginLab 275 Corporation, Northhampton, MA, USA). Two factorial variance analyses with measuring repetitions were performed to evaluate the influence of Fe2+ and flow velocity on biofilm development and structure. In case of non-normality, a Scheirer-Ray-Hare test was applied. Three hypotheses were picked with the following predications:
H1: No differences in structure due to usage of different flow velocities \(u\)
H2: No differences in structure due to usage of different iron concentrations \(c\)
H3: No correlation between both parameters \(u\) and\(c\)
To determine the approval or rejection of the hypotheses, calculated\(p\)-values were compared to a significance level of \(\alpha\)< 0.01, whereby values < \(\alpha\)describe the rejection of the individual hypothesis. Variance analyses were performed in Excel (Excel version 15.11, Microsoft Corporation, Washington, USA).