What is the variable long term returns?
Unfortunately I don't quite understand your question, but if you mean to ask what is the possible range of long-term equity returns, then the answer isn't a very satisfying -- they can very possibly return anywhere from negative 100% (total loss of the entire investment) to positive 1000s of percent, depending on the timeframe and your luck. Prudent expectation for long-term diversified global equity returns for the next 20 years is, in my opinion, somewhere around 3-4% real (post-inflation) return. This is worse than the return from equities over the past 100 years, but better than what I expect from bonds or alternative investments like gold in the same period. You can see my forecast for future returns at http://www.longtermreturns.com/2012/03/20-year-returns-forecast.html -- my expectations did not change substantially in the two months since I made that post, though equities are a tiny bit more attractive now and bonds are a tiny bit less attractive.
I haven't the slightest clue what the more immediate future will bring. Maybe we entering a nasty recession sparked by the break-up of the Euro (or even a depression sparked by US default if the Congress fails to come to a debt ceiling agreement in the coming months). Or maybe right now is your last opportunity to scoop up stocks on the cheap and sell your overpriced bonds before investors realize that the world isn't ending after all and today's stocks are bargains relative to today's bonds. It really could go either way. Anyone who is totally sure of one outcome or the other is lying to you and/or to himself.
But whatever the immediate future brings, the long-term returns from equities are driven by their starting valuations, by capitalism which relies on our innate drive to invent, create, improve, and otherwise increase our productivity, by general population growth, and by avoiding truly world-altering calamities (think Hollywood end-of-the-world scenarios). Current valuations are a mixed bag but certainly not dirt cheap. Capitalism has not been repealed, nor has the human race lost its drive to become smarter, better, and richer. The human population is still growing, though at a slowing pace (which is actually a good thing for sustainability reasons). And while I can't promise you an asteroid won't wipe out a billion human beings tomorrow, I'm staying optimistic on the matter.
For the combination of those reasons I remain generally optimistic about long term returns from equities, though at somewhat lower levels than many have come to expect in the boom times of 1980s and 1990s. I hope to be pleasantly surprised by higher returns than 3-4% real annually, but am not counting on it. I also realize that not even the most prudent expectations are guaranteed to come to pass as investors in pre-1917 Russia found out, for example. The lousy end of the range of possible long-term returns is a total loss of even the most prudently allocated portfolio.