I won't try to summarise all of his points, he isn't trying to prove that stocks are undervalued:
But he certainly goes out of his way to suggest it is not even remotely clear that they are overvalued in any sense.Am I making the case that stocks are under valued? If I did, I would be just as guilty as those who use CAPE to make the opposite case. I am not a market timer, by nature, and any single pricing metric, no matter how well reasoned it may be, is too weak to capture the complexity of the market.
But maybe most usefully for the many, many, many posts on Bogleheads about "am I investing at the peak, what should I do" he provides a CAPE-based market timing spreadsheet so you can try your market timing ideas yourself and see how poorly they work out
http://www.stern.nyu.edu/~adamodar/pc/b ... iming.xlsx
Note that as you trust CAPE more and more (using lower thresholds and adjusting your equity allocation more), you do more and more damage to the end-value of your portfolio