Research based on the discovery of some of Morton's original data by University of Pennsylvania anthropology doctoral student Paul Wolff Mitchell in 2018 argues that Morton was nevertheless guilty of bias, though not in data collection. Mitchell argues that Morton's interpretation of his data was arbitrary and tendentious; he investigated averages and ignored variations in skull size so large that there was significant overlap. A contemporary of Morton, Friedrich Tiedemann, had collected almost identical skull data and drawn conclusions opposite to Morton's on the basis of this overlap, arguing strongly against any conception of a racial hierarchy.