Derby CA, Araujo AB, Johannes CB, Feldman HA, McKinlay JB. Measurement of erectile dysfunction in population-based studies: the use of a single question self-assessment in the Massachusetts Male Aging Study. Int J Impot Res. 2000 Aug 1;12(4):197-204.
Morant SV, Gnanasakthy A. A new approach to the mathematical formulation of lactation curves. Anim Prod Sci. 1989 Oct;49(2):151-62.