Returns the cause-specific single-decrement person-years lived for age interval [Age,Age+AgeInterval). MortHandle is a multiple decrement mortality. If AgeInterval is not specified then it defaults to 1.0. Person-years lived \(_n \sdssf_x\) from Age \(x\) for AgeInterval \(n\) is given by the integral of the cause-specific single-decrement survival fraction \begin{equation} _n \sdssf_{\cause x} = \int_x ^{x+n} \sdsfrac_\cause(a) da \end{equation} Cause is a comma-separated list of cause codes, possibly prefixed by '~' to denote the complement.