Parapunter
The above replies are correct, but overlook the specific problems facing the harrier designers. In order to produce efficient vertical thrust, the gas flowing from the engine nozzles requires a reasonably clear path vertically downwards. This required the use of high wings. But high wings combined with a fairly high wing sweep angle would produce unacceptably strong lateral stability. The addition of anhedral both on the wings and tailplane, reduced the larteral stability, thereby restoring a reasonable degree of roll response.