The Falling Weight Deflectometer data for load transfer efficiency at joints in Jointed Concrete Pavement (JCP) must be properly analyzed and interpreted in order to prevent misleading results. Some parameters affecting pavement deflection are the pavement layer moduli, Poisson's ratios, thicknesses, and layer interaction. All of these must be considered to accurately “backcalculate” moduli from deflections. Joints add even more variables which affect the deflection measurement such as loss of support due to pumping at or near the joint. It is this parameter which will be discussed in this paper. First, a methodology for determining load transfer efficiency at a joint with subbase support will be given. Second the effects of loss of subbase support will be discussed and a methodology, with qualifications, given to determine load transfer at a joint that has loss of subbase support.