Skew Quads

$P,Q,R,$ and $S$ are four coplaner points that lie on the sides $\overline{AB},\overline{BC},\overline{CD},$ and $\overline{DA},$ respectively, of a skew quadrilateral. Then what is $\frac { \lvert\overline{AP}\rvert }{ \lvert\overline{PB}\rvert } \cdot \frac { \lvert\overline{BQ}\rvert }{ \lvert\overline{QC}\rvert } \cdot \frac { \lvert\overline{CR}\rvert }{ \lvert\overline{RD}\rvert } \cdot \frac { \lvert\overline{DS}\rvert }{ \lvert\overline{SA}\rvert }?$