Here is a graph of NASDAQ Composite earnings since 1995:

Source: Bloomberg

The several trillion dollar question is whether a tripling of these earnings in the last five years is real and sustainable after they were kind of flat/bounced around in the 60-90 range for the previous 15 years?  Did something real and sustainable happen in 2010 that permanently elevated earnings to a much higher plateau or are they artificially inflated by free money?  Even if the current level of earnings is real and sustainable, one could argue that 20x earnings of 170 for the NASDAQ is pretty fully valued, i.e. 3,400 is fair value.  (The market is currently trading at 5,100.)  Interestingly, if earnings are, in fact, artificially inflated and will revert to a more believable 100 as rates (supposedly) rise in the next couple of years, then one would more rationally be looking at a much nastier valuation, i.e. 2,000 or a bit more, which is where the market spent most of its time from after the .com crash until 2010 when the printing presses transitioned into full swing.  The NASDAQ is just the most prominent bellwether for what risk asset valuations look like across many asset classes....

That leads one to ask if all the companies in the NASDAQ really became three times more profitable in the last five years than they were in the previous fifteen OR are those profits artificial, or at least ephemeral, and will they dissipate in coming years if there is a return to some sort of 'normalcy'/sustainability?  Your answer to that question will clearly drive where you want to place your bets for the next few years.  Good luck.  In Janet Yellen We Trust!