Graham JE, Rouse M, Twiss J, McKenna SP, Vidalis AA. Greek adaptation and validation of the Ankylosing Spondylitis Quality of Life (ASQoL) measure. Hippokratia. 2015;19(2):119-24.
McKenna S, Doward LC. Measuring quality of life in ankylosing spondylitis. Best Pract Res Clin Rheumatol. 2008 Jan 1;6(2):12-4.
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