100% of the year-to-date returns were contained within roughly 50% of trading weeks. (15 positive/14 negative weeks)
78.5% of the year-to-date gains have occurred since May 20th.
100% of the gains for the year have occurred since April.
These gains have also come at a time when corporate profits are slowing; economic growth remains weak and geopolitical tensions have been on the rise. UBS published a research piece last week entitled 'We are worried' which stated:
"Firstly we are concerned about valuations. We show that equity markets are stretched (e.g., more than 80% of the S&P rally since last year is due to re-rating), but we also find that the fixed income market has become quite rich (we have been overweight European peripherals for more than a year on valuation grounds, we show that this argument no longer holds), and the same is true of the credit market.
Second, because capital has been flowing rapidly into risky assets, we document that argument and here too find evidence that the market might be ahead of itself. We read the market reaction last week to the Portuguese news as a sign that the market is indeed too complacent and could correct rapidly."