Thomas A, Danon L, Christensen H, Northstone K, Smith D, Nixon E, Trickey A, Hemani G, Sauchelli S, Finn A, Timpson N, Brooks-Pollock E. Limits of lockdown: characterising essential contacts during physical distancing. Wellcome Open Res. 2021 May;6:116. doi: 10.12688/wellcomeopenres.16785.1
Phanikumar CV, Maitra B. Willingness-to-pay and preference heterogeneity for rural bus attributes. J Transp Eng A-Syst. 2007 Jan;133(1).
López MV, Rivero E, Serra C, Campo M, Raurich M, Bonfill X. Health survey in health care professionals in Barcelona. Arch Prev Riesgos Laborales. 1998;1(2):55-62.