Phillips C, White RP, Shugars DA, Zhou X. Risk factors associated with prolonged recovery and delayed healing after third molar surgery. J Oral Maxillofac Surg. 2003 Dec 1;61(12):1436-48.
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