highly significantp < 0.001
The protrusion features proA and proX contributed the least to models; however, including these variables did increase the R 2 (MLR6 = 0.4776; MLR4 = 0.4648) and decrease the root mean squared error of predictions (MLR6 = 0.1054; MLR4 = 0.1322), and were always highly significant (p < 0.001).