Propagation conditions are frequently assessed by making a single measurement of the vertical refractivity and injecting this profile into a propagation model from which the two-dimensional propagation factor field is calculated. Such an assessment tacitly assumes lateral homogeneity of the refractivity environment. That is, the refractive index is assumed to vary only as a function of height above the Earth's surface. Hitherto, the authors, using only case studies, have determined errors in propagation assessment employing the above assumptions. The objective of this paper is to characterize the errors in the propagation factor field using a statistical database of multiple arrays of refractivity profiles covering many days. In this effort, errors in the propagation factor field at 1, 3, and 10 GHz are derived for the case in which single refractive index profile measurements are used to calculate the two-dimensional propagation factor field. This error field is subsequently compared with the benchmark or truth propagation factor field calculated using an array of refractivity profiles. The errors are statistically deduced by combining measurements from 30 days over defined two-dimensional areas. The methodology for which the above type of propagation assessment is addressed may also be used to establish temporal and lateral spacing requirements employing similar statistical databases. ¿ 1998 American Geophysical Union