18. April H. Crusco y Christopher G. Wetzel, «The Midas Touch: The Effects of Interpersonal Touch on Restaurant Tipping», Personality and Social Psychology Bulletin 10, nº 4 (diciembre de 1984), pp. 512-517; Céline Jacob y Nicolas Guéguen, «The Effect of Physical Distance Between Patrons and Servers on Tipping», Journal of Hospitality & Tourism Research 36, nº 1 (febrero de 2012), pp. 25-31.