Table 21 shows the final shipment size models (in pounds) used to address the endogeneity between the mode choice and the shipment size. The instrumental variable is the great circle distance in miles. The functional forms are shown in Equations (14) and (15). These models, though they have lower R2, were able to address the endogeneity effectively due to higher t-stat value, which shows the explanatory power of the variable. Some commodities are grouped at 2-digit SCTG to improve the model estimates. The shipment size model for coal (SCTG 15) could not be presented, as it did not pass the disclosure requirements.
Shipment Size Models
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