Christensen T, Riis AH, Hatch EE, Wise LA, Nielsen MG, Rothman KJ, Toft Sorensen H, Mikkelsen EM. Costs and efficiency of online and offline recruitment methods: a web-based cohort study. J Med Internet Res. 2017 Mar 1;19(3):e58. doi: 10.2196/jmir.6716
Brodtkorb T, Kogler GF, Arndt A. The influence of metatarsal support height and longitudinal axis position on plantar foot loading. Clin Biomech (Bristol, Avon). 2008;23(5):640-7.
Reed (Earnshaw) SR, Reed JH, Stuhldreher TJ. Transaction costs, taxes, and portfolio revision. J Contemp Bus Issue. 1997;5:40-8.