  Election data represent a precious source of information to study human
behavior at a large scale. In proportional elections with open lists, the
number of votes received by a candidate, rescaled by the average performance of
all competitors in the same party list, has the same distribution regardless of
the country and the year of the election. Here we provide the first thorough
assessment of this claim. We analyzed election datasets of 15 countries with
proportional systems. We confirm that a class of nations with similar election
rules fulfill the universality claim. Discrepancies from this trend in other
countries with open-lists elections are always associated with peculiar
differences in the election rules, which matter more than differences between
countries and historical periods. Our analysis shows that the role of parties
in the electoral performance of candidates is crucial: alternative scalings not
taking into account party affiliations lead to poor results.
