From memory I think there is some truth to the fact that all Harrier "probablity of mishap" statistics are an order of magnitude worse than most fast jets, be they single or twin engine. No doubt those in the know may comment, but it is fair to say that they are a bit of a special case. If I was to speculate, I'd hazard its because it is a) single engined, b) has an extremely high peformance (power/weight) engine which is consequently less reliable than "ordinary" turbofan/jets (e.g. than a hawk adour for example), and c) has very poor glide characteritics following a engine failure.