Williams RE, Bosnic N, Sweeney CT, Duncan AW, Levine KB, Brogan M, Cook SF. Prevalence of opioid dispensings and concurrent gastrointestinal medications in Quebec. Pain Res Manag. 2008;13(5):395-400.
Williams VSL. The "unbiased" anchor: bridging the gap between DIF and item bias. Appl Meas Educ. 1997;10(3):253-67. doi: 10.1207/s15324818ame1003_4