Gomersall T, Spencer S, Basarir H, Tsuchiya A, Clegg J, Sutton A, Dickinson K. Measuring quality of life in children with speech and language difficulties: a systematic review of existing approaches. Int J Lang Commun Disord. 2015 Jul;50(4):416-35. doi: 10.1111/1460-6984.12147
Phanikumar CV, Maitra B. Willingness-to-pay and preference heterogeneity for rural bus attributes. J Transp Eng A-Syst. 2007 Jan;133(1).