AV-8B vs GR-5/7 Attrition

Does anyone know the comparitive loss rates for the AV-8B and the Harrier GR-5/7. It seems to me that the USMC has a far higher loss rate, but I want to know if this can be confirmed by the losses per flight hour stats. If the USMC does lose more Harriers, does anyone know the reasons. Also how does Harrier attrition compare to other single engined strike/ fighter aircraft. I suspect it is worse and wonder what that says about VSTOL technology, or more particularly, Rolls Royce engine design.