Luciano JV, Barrada JR, Aguado J, Osma J, García-Campayo J. Bifactor analysis and construct validity of the HADS: a cross-sectional and longitudinal study in fibromyalgia patients. Psychological Assessment. 2014 Jun;26(2):395-406.
Merrill RM, Madanat H, Layton JB, Hanson CL, Madsen CC. Smoking prevalence, attitudes, and perceived smoking prevention and control responsibilities and behaviors among physicians in Jordan. Int Q Community Health Educ. 2006;26(4):397-413.