APA (7th ed.) Citation

Valderas, J., Starfield, B., Sibbald, B., Salisbury, C., & Roland, M. (2009). Defining comorbidity: Implications for understanding health and health services.

Chicago Style (17th ed.) Citation

Valderas, J., B. Starfield, B. Sibbald, C. Salisbury, and M. Roland. Defining Comorbidity: Implications for Understanding Health and Health Services. 2009.

MLA (9th ed.) Citation

Valderas, J., et al. Defining Comorbidity: Implications for Understanding Health and Health Services. 2009.