Table 9.

Error Metrics for pH interpolation methods, generated via leave-one-out cross-validation.

Method	r	RMSE	MAE	MBE	MSA
NN	0.78	0.55	0.35	0.007	0.029
IDW-OR	0.84	0.46	0.30	0.007	0.027
IDW-OM	0.84	0.46	0.30	0.008	0.027
OK	0.81	0.49	0.33	0.001	0.031
OK-ZN	0.84	0.45	0.30	0.001	0.028

The best interpolation methods for each metric are highlighted in bold. Metrics: RMSE = Root Mean Square Error, MAE = Mean Absolute Error, MBE = Mean Bias Error, MSA = Median Symmetric Accuracy. Methods: NN = nearest neighbour; IDW-OR = inverse distance weighting, RMSE-optimised; IDW-OM = inverse distance weighting, MAE-optimised; OK = ordinary kriging, unconstrained nugget; OK-ZN = ordinary kriging, zero nugget.