Volume Bias Adjustment to AW and PL species groups Sample Clauses

Volume Bias Adjustment to AW and PL species groups. To address the over-estimation of gross merchantable volume predicted by GYPSY for the AW and PL species groups, an adjustment method to remove the bias was presented to and approved by ASRD.26, 43 In summary, simple linear regressions were fit between PSP gross merchantable volume (dependent variable) and GYPSY predicted gross merchantable volume (independent variable) for those species whose residuals were tested to be significantly different from zero. The overestimation bias (as determined by the regression slope) for AW was 10% across most yield groups. However, due to noted differences in yield groups 4 and 7, regressions were fit separately and resulted in biases of 15% for yield group 7 and 23% for yield group 4. PL overestimation averaged about 6% across all yield groups. Individual GYPSY projections were adjusted by multiplying predicted volumes by the regression slope for each species and yield group class. Adjusted residuals were then plotted against predicted GYPSY volumes to illustrate the removal of bias following adjustment (Figure 14, Figure 15).