Cole JA, Rothman KJ, Cabral HJ, Zhang Y, Farraye FA. Incidence of IBS in a cohort of people with asthma. Dig Dis Sci. 2007 Feb 28;52(2):329-35.
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
Norton EC, Zarkin GA, Calingaert B, Bradley CJ. The effect of maternal substance abuse on the cost of neonatal care. Inquiry. 1996;33(3):247-57.