Dr. M. H. Ali
SSO
BINA
I. Abustan
Prof.
USM, Malaysia
Model evaluation, Statistical indicators, Model performance
Knowledge Management
Efficiency
Proposed new index
Percent mean absolute relative error (PMARE)
It is the ‘mean absolute relative error’, expressed in percentage.
...........................(1)
Where, “Abs’ indicates ‘absolute value (of the difference between observed and simulated value). Theoretically, the value of PMARE ranges from 0% to ∞ (positive infinity). The interpretation and characterization of the index are discussed later.
Data for comparison of indices
To test the statistics and indices, both the field observed data and simulated random data were used.
Simulation comparison with field observed data
Field data are originated from wheat experiment, where diverse irrigation treatments were applied representing different strategies of deficit irrigation. Simulation was performed using AquaCrop model of FAO (Steduto et al. 2009). Before simulation, calibration of the model was performed using one year data. The model AquaCrop produces inferior simulations at extreme dry condition (herein referred as ‘odd simulation’– sometimes referred in the literature as ‘outliers’), which is a common problem in many models.
Simulation comparison with Random data
To show the behavior of the indices under different patterns of data series, values of O and P were created (generated) using a random data generator. More specifically, 3 sets of random data of size n=20 were generated separately for O and P using a random number generator (RANDOM.ORG, 2012) . The randomness comes from atmospheric noise.
Calculation of the indices
The indices (earlier used - EF, d, dr and r) were calculated using Microsoft spreadsheet following the equations mentioned earlier.
J. of Natural Resour. and Dev., 04: 1-9, (2014)
Journal