APA (7th ed.) Citation

Knowles, S., & Sheldon, B. (2007). Sex ratios: Human twins and fraternal effects.

Chicago Style (17th ed.) Citation

Knowles, S., and B. Sheldon. Sex Ratios: Human Twins and Fraternal Effects. 2007.

MLA (9th ed.) Citation

Knowles, S., and B. Sheldon. Sex Ratios: Human Twins and Fraternal Effects. 2007.

Warning: These citations may not always be 100% accurate.