A Peculiar Sample: A Reply to Steckel and Ziebarth
指出Steckel和Ziebarth在识别奴隶贸易商时存在分类错误，低估了贸易商运输的奴隶比例，导致其选择偏差估计被削弱。
Richard Steckel and Nicolas Ziebarth (2016) find that biases in height by age imposed by traders versus non-traders were negligible. Importantly, their method of identifying traders differs from that of Jonathan Pritchett and Herman Freudenberger (1992). Using a sample of inward coastwise manifests for the port of New Orleans, we show that Steckel and Ziebarth made errors classifying shippers, that they underestimate the relative number of slaves shipped by traders, and that their empirical estimates of selection bias are attenuated towards zero.