I have to admit I've seen a variety of numbers, mostly ranging from 26-40. The 34 I quoted was based on info supplied by a freeper today for the S&P 500 as of Friday's close and confirmed from a separate source
here. These numbers are in line with numerous other citations I've seen. My guess is the variation is due to how earnings are calculated: trailing versus projected, pro forma versus GAAP, etc. What is the source of the 18 you mentioned?
"The 34 I quoted was based on info supplied by a freeper today for the S&P 500 as of Friday's close..." That P/E figure came from BigCharts.com, you can click on this URL:
http://bigcharts.marketwatch.com/quickchart/quickchart.asp?symb=sp500&sid=0&o_symb=sp500