Freight Distribution Model Predictions Compared: Some Further Evidence

Abstract

This paper reviews the comments made by Gordon (1979) on the paper by Pitfield (1978) and, where appropriate, provides further evidence. In particular, intrazonal error in the gravity model is examined for twenty-eight commodities and it is concluded that the error is not as serious as implied. There is no evidence for bias in the diagonal elements of the distance matrix, and a deterrence function, used as an alternative to the negative-power function, does not provide better predictions. It is also shown that the PEP statistic is not corrected for scale in the same way as the other standardised statistics and so its correlation with these other statistics is strongly influenced by the scale of entries in the matrices. Minor points are made on the questions of speed of gravity-model convergence as β → ∞ and on the suitability of the χ2 test.