The phrase "determinative role" means that something has the power or ability to greatly influence or make a final decision on a particular outcome or result. Full definition
Considering the important and sometimes crucially determinative role of journalism in public policy debate, I think it's reasonable to wonder why journalists» notebooks and professional communications are not transparently available to the public on demand. (realclimate.org)
Impact of first impression in business field can't be overestimated: even irrelevant to the hiring process details can play determinative role. (resumewritingservice.biz)
In the final chapter, Rosalind Ladd, professor of philosophy at Wheaton College, writes: «It is imperative that women take an active and determinative role in decision making for themselves.» (newscientist.com)