Also in 2016, a meta-analytic synthesis of prior empirical research on grit by Crede, Tynan, and Harms [13] summarized data from 88 independent samples and over 66,000 individuals and found that grit is only weakly related to success and almost identical to the personality trait known as conscientiousness. Crede et al. conclude that the contribution of grit to the prediction of success is very limited. Crede et al., also noted that the combination of passion and perseverance into an overall grit construct could not be justified.

(http://www.autoadmit.com/thread.php?thread_id=3682759&forum_id=2#33837676)