To avoid concerns about overparameterisation and spurious correlations between multiple variables, a PCA was conducted. The identified factors, which retained the patterns of the original variables, were to be introduced as new variables into the latter regression model. The correlations between the obtained port activity variables ranged from -0.295 to 0.969 (Table 5). As anticipated, most of the nine variables are heavily correlated. The first three, out of nine components, account for more than 70% of the intrinsic variance of the data fulfilling the Kaiser criterion with eigenvalues over 1.