Check the tags for prior versions. My consistent basic points have been:

1. Smart $ unlikely to pay above 18x SPX forward earnings; and
2. Citigroup Economic Surprise index would have to move into decently positive territory for a strong breakout above 2015 highs.

What has happened? According to WSJ data, the forward earning estimate of SPX was near 120 in mid March, then declined. There are some odd jumps in this data so take any individual reading with grain of salt. For example, after listing about 118.50 the first week of April and then 117.50 the second week, somehow it was 112.50 the week of 4/15. This made the P/E jump above 18 for one week. But with earnings back to 117.50 and 117, the next 2 weeks, the P/E has returned to 17.8 for the week of 4/22 and 17.65 the week of 4/29.

So, the point here is that the only time SPX appeared to move above 18x forward earnings was an odd skip in the data. Otherwise since tracking this from early March the my spreadsheet looks like this:

Date Est earnings Est P/E
3/11 120.93 16.72
3/18 120.21 17.05
3/25 116.01 17.55
4/01 118.51 17.49
4/08 117.61 17.41
4/15 112.47 18.50
4/22 117.50 17.80
4/29 117.01 17.65

So basically the market has complied with this idea so far, and SPX 18x has been resistance. Maybe Bloomberg (what i used to use and track daily when at a hedge fund) has better data.

Anyway using the current estimate, 17x support 1989 and 18x resistance 2106.

NDX 17.95x, so 18x level breaking slightly. 17x 4111, 18x 4353.
INDU 16.93x, so possible resistance at 17x. In fact, the two weeks near the highs were 17.06 and 17.15. 17x even is now 17845.
RTY 17.52x so 17 1096x and 18x 1160.

Yardeni PDF of the Citigroup Economic Surprise index. This stalled at the zero line so it should be no surprise that markets have stalled as well.