A. Plœtz, "Lebensdauer der Eltern und Kindersterblichkeit," Archiv für Rassen-u Gesellschafts-Biologie, VI (1909), pp. 33-43.

Or it may be supposed that the environment is so good as to make a non-selective death less likely, and therefore such deaths as do occur must more frequently be selective.

Hibbs, Henry H., Jr., Infant Mortality: Its Relation to Social and Industrial Conditions, New York, 1916.