Phanikumar CV, Maitra B. Willingness-to-pay and preference heterogeneity for rural bus attributes. J Transp Eng A-Syst. 2007 Jan;133(1).
Knox D, Gibson L, Zusman ME, Gallmeier C. Why college students end relationships. Coll Stud J. 1997 Jan 1;31(4):449-52.