Abstract INTRODUCTION IT WAS concluded by Bohren, Rapp and Arvidson (1952) that no genetic differences in rate of egg size increase existed during the early fall months among the families and breeds studied. In addition, the regression of egg weight on weeks of age appeared to approach linearity. In view of these and other observations it was proposed that egg weights be taken at one time in the early part of the laying year and that a linear correction factor based on the linear regression of egg weight on age be used to approximate the egg weights of pullets at a common age. The remaining difference in egg weight between the pullets was then considered to be a reasonable estimate of the genetic difference in egg size to be used in the selection of breeders. The purpose of this study was to further consider these observations with a larger quantity of…