Overall accuracy of data was assessed by comparing species lists for specific areas with GAP predictions of species present and absent.
Incidences of GAP predictions of non-occurrence and actual species presence were considered errors of ommission. Incidences of GAP predictions of species occurrence and species actual non-presence were considered errors of commission. Accuracies obtained in the way likely increase with the size of the area compared to GAP predictions. Due to lack of complete species inventories, errors of commission may be considered less reliable estimates than errors of omission.
More information may be obtained in Kramer et al. 2003.