Active, but not passive cigarette smoking was inversely associated with mammographic density.

MLA

Butler, Lesley, et al. “Active, but Not Passive Cigarette Smoking Was Inversely Associated with Mammographic Density.” Cancer Causes & Control, vol. 21, no. 2, Feb. 2010, pp. 301–11. EBSCOhost, https://doi.org/10.1007/s10552-009-9462-4.

APA

Butler, L., Gold, E., Conroy, S., Crandall, C., Greendale, G., Oestreicher, N., Quesenberry, C., Habel, L., Butler, L. M., Gold, E. B., Conroy, S. M., Crandall, C. J., Greendale, G. A., Quesenberry, C. P., Jr, & Habel, L. A. (2010). Active, but not passive cigarette smoking was inversely associated with mammographic density. Cancer Causes & Control, 21(2), 301–311. https://doi.org/10.1007/s10552-009-9462-4

Chicago

Butler, Lesley, Ellen Gold, Shannon Conroy, Carolyn Crandall, Gail Greendale, Nina Oestreicher, Charles Quesenberry, et al. 2010. “Active, but Not Passive Cigarette Smoking Was Inversely Associated with Mammographic Density.” Cancer Causes & Control 21 (2): 301–11. doi:10.1007/s10552-009-9462-4.