Table 3.
Statistical measures of IDW interpolations of groundwater nitrate concentration in Bavaria, averaged over parameter number of total observation points (m), number of observation points used for weighting (n), and IDW exponent (p)
| Parameter | Mean | MINa | MAX | SD | Q90 | MAE | RMSE | COR | AaT | |
|---|---|---|---|---|---|---|---|---|---|---|
| Value | mg NO3/l | - | % | |||||||
| m | 1412 | 28.51 | 3.2 | 68.5 | 13.52 | 45.82 | 6.60 | 9.09 | 0.814 | 4.28 |
| 3531 | 28.50 | 3.1 | 69.3 | 13.80 | 46.12 | 5.93 | 8.29 | 0.847 | 4.54 | |
| 7063 | 28.50 | 3.1 | 69.8 | 13.96 | 46.34 | 5.40 | 7.63 | 0.872 | 4.50 | |
| n | 4 | 28.50 | 3.0 | 71.6 | 14.19 | 46.75 | 6.01 | 8.50 | 0.839 | 5.23 |
| 8 | 28.51 | 3.1 | 69.3 | 13.79 | 46.14 | 5.94 | 8.31 | 0.845 | 4.48 | |
| 12 | 28.51 | 3.2 | 68.3 | 13.60 | 45.84 | 5.96 | 8.27 | 0.847 | 4.14 | |
| 16 | 28.51 | 3.2 | 67.5 | 13.47 | 45.65 | 5.99 | 8.27 | 0.847 | 3.92 | |
| p | 1 | 28.52 | 3.3 | 64.3 | 13.32 | 45.44 | 6.05 | 8.29 | 0.845 | 3.65 |
| 1.5 | 28.50 | 3.2 | 67.2 | 13.51 | 45.72 | 5.93 | 8.20 | 0.849 | 3.98 | |
| 2 | 28.51 | 3.1 | 70.1 | 13.74 | 46.06 | 5.88 | 8.21 | 0.849 | 4.39 | |
| 4 | 28.51 | 3.0 | 75.1 | 14.47 | 47.15 | 6.05 | 8.24 | 0.835 | 5.75 | |
| Reference population | 28.49 | 2.7 | 81.1 | 15.53 | 48.77 | 8.29 | ||||
aMIN: minimum; MAX: maximum; SD: standard deviation; Q90: 5th–95th interpercentile range; MAE: mean absolute error; RMSE: root mean square error; COR: Pearson correlation coefficient; AaT: percentage area above threshold 50 mg NO3/l. Mean, SD, Q90, MAE: averaged over 16 (for m) or 12 (for n, p) parameter combinations × 100 interpolations × (70,634 − m) grids; MIN, MAX: minimum, maximum of 16 (for m) or 12 (for n, p) parameter combinations × 100 interpolations × (70,634 − m) grids; RMSE, COR, AaT: averaged over 16 (for m) or 12 (for n, p) parameter combinations × 100 interpolations