Nelson, Lorene M., Caroline M. Tanner, Stephen K. Van Den Eeden, and Valerie M. McGuire. "Measurement and Analysis." Neuroepidemiology: From principles to practice. : Oxford University Press, 2004-01-15. Oxford Scholarship Online. 2009-09-01. Date Accessed 19 Jun. 2013 <http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780195133790.001.0001/acprof-9780195133790-chapter-03>.
Nelson, L., Tanner, C., Van Den Eeden, S., & McGuire, V.(2004-01-15). Measurement and Analysis. In Neuroepidemiology: From principles to practice. : Oxford University Press. Retrieved 19 Jun. 2013, from http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780195133790.001.0001/acprof-9780195133790-chapter-03.
Nelson, Lorene M., Caroline M. Tanner, Stephen K. Van Den Eeden, and Valerie M. McGuire. "Measurement and Analysis." In Neuroepidemiology: From principles to practice. : Oxford University Press, 2004-01-15. http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780195133790.001.0001/acprof-9780195133790-chapter-03.
Nelson LM, Tanner CM, Van Den Eeden SK, McGuire VM. Measurement and Analysis. In: Nelson LM, Tanner CM, Eeden SVD, McGuire VM. Neuroepidemiology: From principles to practice. Oxford University Press; 2004. http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780195133790.001.0001/acprof-9780195133790-chapter-03. Accessed June 19, 2013.