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.
Mansfield CA, Pattanayak SK, McDow W, MacDonald R, Halpin P. Shades of green: measuring the value of urban forests in the housing market. J Forest Econ. 2005 Dec;11(3):177-99. doi: 10.1016/j.jfe.2005.08.002