Schmitt CL, Allen JA, Kosa KM, Curry LE. Support for a ban on tobacco powerwalls and other point-of-sale displays: findings from focus groups. Health Educ Res. 2015 Feb;30(1):98-106. doi: 10.1093/her/cyu046.
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