We thus tried to encompass possible combinations of words that studied our topic. After continuous checking processes, we then also filtered articles, removing those classified under unrelated categories, which were mainly those from medical disciplines. In addition, we checked the remaining articles so as to filter those related to the topic. We were therefore able to obtain the main figures and overall research configuration on boards of directors before delving into certain core intellectual nodes, subtopics or publications. Systematic filtering of registers was then carried out to ensure consistency in authors and citations. The articles obtained were published up to 2016 (Danvila-del-Valle et al., 2019)..