Godwin, M., Ruhland, L., Casson, I., MacDonald, S., Delva, D., Birtwhistle, R., . . . Seguin, R. (2003). Pragmatic controlled clinical trials in primary care: The struggle between external and internal validity. BioMed Central.

Godwin, Marshall, Lucia Ruhland, Ian Casson, Susan MacDonald, Dianne Delva, Richard Birtwhistle, Miu Lam, and Rachelle Seguin. Pragmatic Controlled Clinical Trials in Primary Care: The Struggle between External and Internal Validity. BioMed Central, 2003.

Godwin, Marshall, et al. Pragmatic Controlled Clinical Trials in Primary Care: The Struggle between External and Internal Validity. BioMed Central, 2003.