Measurements of independent fission product yields from thermal-neutron fission of 235U, 239Pu, 233U, and 241Pu have been compared with expected yields from a semiempirical analytical model. A general correlation between the experimental/theoretical ratio and the distance of the nuclide from Zp, the most probable charge in a fission product mass chain, has been constructed. This correlation can serve as a basis for assigning uncertainties to theoretical yield estimates.