In statistics, an inverted bell curve is a term used loosely or metaphorically to refer to a
bimodal distribution that falls to a trough between two peaks, rather than (as in a standard
bell curve) rising to a single peak and then falling off on both sides.[1]
References
^E.g., see Gensheimer, Leah K.; Diebold, Charles T. (2014–2015), "Bimodal Inverted Bell Grade Distribution: Implications for Instruction and Student Retention", Journal of College Student Retention: Research, Theory and Practice, 16 (3): 307–324,
doi:
10.2190/CS.16.3.a,
S2CID144272500.