“Students on the pass-fail system did not show any significant effects from first exam grades, but overall they received significantly lower grades than those on the traditional grading system.” (p.71)

Thayer, R. E. (1973). Do Low Grades Cause College Students to Give Up? The Journal of Experimental Education, 41(3), 71–73. doi: 10.1080/00220973.1973.11011413