Landy distinguishes between the "commercial" and "academic" discussion of EI, basing this distinction on the alleged predictive power of EI as seen by each of the two. According to Landy, the former makes expansive claims on the applied value of EI, while the latter is trying to warn users against these claims. As an example, Goleman (1998) asserts that "the most effective leaders are alike in one crucial way: they all have a high degree of what has come to be known as emotional intelligence. ...emotional intelligence is the sine qua non of leadership". In contrast, Mayer (1999) cautions "the popular literature's implication—that highly emotionally intelligent people possess an unqualified advantage in life—appears overly enthusiastic at present and unsubstantiated by reasonable scientific standards." Landy further reinforces this argument by noting that the data upon which these claims are based are held in "proprietary databases", which means they are unavailable to independent researchers for reanalysis, replication, or verification. Furthermore, Murensky (2000) states it is difficult to create objective measures of emotional intelligence and demonstrate its influence on leadership as many scales are self-report measures.