Shorts provide support because a proportion of shorters take profit by covering (buying) at every dip. A proportion also cover in panic at every rally. The curent level of shorting is providing massive support to equity markets which will only be able to decline significantly when those shorts are covered. A blow-out rally would do that. I would like to be able to estimate what price each index would rise to if a short-covering blow-out rally occurred. At that point the market would be massively over-priced and under-supported and susceptible to a sharp correction or mini-crash which is precisely what happened in 1987.