For probability distributions which don't have an explicit density function expression, but have an explicit [[quantile function]] expression, <math>Q(p)</math>, then <math>h(Q)</math> can be defined in terms of the derivative of <math>Q(p)</math> i.e. the quantile density function <math>Q'(p)</math> as <ref>{{Citation |last1=Vasicek |first1=Oldrich |year=1976 |title=A Test for Normality Based on Sample Entropy |journal=[[Journal of the Royal Statistical Society, Series B]] |volume=38 |issue=1 |jstor=2984828 |postscript=. }}</ref>{{rp|54–59}} | For probability distributions which don't have an explicit density function expression, but have an explicit [[quantile function]] expression, <math>Q(p)</math>, then <math>h(Q)</math> can be defined in terms of the derivative of <math>Q(p)</math> i.e. the quantile density function <math>Q'(p)</math> as <ref>{{Citation |last1=Vasicek |first1=Oldrich |year=1976 |title=A Test for Normality Based on Sample Entropy |journal=[[Journal of the Royal Statistical Society, Series B]] |volume=38 |issue=1 |jstor=2984828 |postscript=. }}</ref>{{rp|54–59}} |