Aguado J, Campbell A, Ascaso C, Navarro P, Garcia-Esteve L, Luciano JV. Examining the factor structure and discriminant validity of the 12-Item General Health Questionnaire (GHQ-12) among Spanish postpartum women. Assessment. 2012 Dec 19;19(4):517-25.
Watson V, Ryan M. Exploring preference anomalies in double bounded contingent valuation. J Health Econ. 2007 May 1;26(3):463-82. doi: 10.1016/j.jhealeco.2006.10.009