Overall accuracy of data was assessed by comparing species lists for specific areas and results of breeding bird surveys with GAP predictions of species present and absent for areas and breeding bird survey routes. Incidences of GAP peredictions of non-occurrence and actual species presence was considered an error or ommission. Incidences of GAP predictions of species occurrence and species actual non-presence was considered an error of commission. Accuracies 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 omission.
More information may be obtained in Kramer et al. 2003.