Any correlation that produces straight lines interests me. This one is intriguing. You'd think that if the dollar is up the market may be that much more down, but not necessarily so.
The dollar was strong in 2000-2001 and again now, but not so much in 2007-2008. But dividing the S&P by the dollar index produces a perfectly straight line through all 3 tops.
So for now it looks like S&P down, dollar up, or both is the trend for the next year, year and a half.