Lehman, Harvey Christian. "15. Achievement by Decades". Age and Achievement, Princeton: Princeton University Press, 1953, pp. 241-252. https://doi.org/10.1515/9781400886753-017
Lehman, H. (1953). 15. Achievement by Decades. In Age and Achievement (pp. 241-252). Princeton: Princeton University Press. https://doi.org/10.1515/9781400886753-017
Lehman, Harvey Christian. "15. Achievement by Decades" In Age and Achievement, 241-252. Princeton: Princeton University Press, 1953. https://doi.org/10.1515/9781400886753-017