Rater biases are of interest to behavior genetic researchers, who often use ratings data as a basis for studying heritability. Inclusion of multiple raters for each sibling pair (M. Bartels, D. I. Boomsma, J. J. Hudziak, T. C. E. M. van Beijsterveldt, & E. J. C. G. van den Oord, 2007) is a promising strategy for controlling bias variance and may yield information about sources of bias in heritability studies. D. A. Kenny's (2004) PERSON model is presented as a framework for understanding determinants of rating reliability and validity. Empirical findings on rater bias in other contexts provide a starting point for addressing the impact of rater-unique perceptions in heritability studies. However, heritability studies use distinctive rating designs that may accentuate some sources of bias, such as rater communication and contrast effects, which warrant further study.