After the NBER study was published in the peer-reviewed "Journal of Political Economy", a 2019 paper by Princeton University political scientists disputed the findings by Fryer, saying that if police had a higher threshold for stopping whites, this might mean that the whites, Hispanics and blacks who were included in Fryer's data are not similar. A further October 2020 comment on the NBER paper by Steven Durlauf and (Nobel Prize in Economics recipient) James Heckman of the Harris School of Public Policy Studies at the University of Chicago stated, "n our judgment, this paper does "not" establish credible evidence on the presence or absence of discrimination against African Americans in police shootings." Fryer responded by saying Durlauf and Heckman erroneously claim that his sample is "based on stops". Further, he states that the "vast majority of the data...is gleaned from 911 calls for service in which a civilian requests police presence."