We further investigated the occurrence of data degeneracy. The standard deviation of PCE in a degeneracy distributed as shown in Fig. . The median was 1.54%, and the maximum Please do not adjust margins Please do not adjust margins difference was 12.30% (Fig. ). The total degenerated unique points were 6446, consisting of 20695 vectors. The number of vectors in a degeneracy mainly was 2, and the maximum was 60 (Fig. ). While these distributions did not change largely by different splitting methods (Fig. ), the number of data degeneracies increased as the splitting order increased (Fig. ). There are 6441 degenerated unique points consisting of 20677 vectors at the beginning. This means that the original database contains the same information at different records, probably due to not fully capturing process variables in the database. Such data degeneracy causes the limitation of predictive performance. The number of degeneracies increases depending on the split order because the data may become the same vector, as illustrated in Fig. . If the degeneracy occurs in data with a large difference in PCE, it will harm the regression. The split method also has a positive effect on measuring the closeness between data, and thus there is a suitable balance between positive negative effects.