In the five US recessions since 1980, on average stock market valuations have gone from 16 to 11 times forward earnings, always ending no higher than 14x.
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Can you confirm the data points you are using?...
So statement of "16 to 11" is interesting, the market is at 20x not 16. Is this peak to bottom? (historically)?

The calculations weren't mine, I was quoting from an FT article which came out the day of my post so the market levels should have matched the comments, within a day. The main thing to note is the word "forward" earnings. Yes, they were talking about peak to trough drops.

My own calculations look at things more from valuation levels. A post of mine from four days ago: mungofitch replies on Lows and CAPE

Precis: I have no idea what will happen, but IF valuations based on smoothed real earnings revert to what has been the normal valuation levels in the last 20-30-40 years, you'd expect the S&P to be at roughly 3650-4320 these days, a drop of about 26-38% from here. Emphasis on the "IF"--this is an observation of what the arithmetic says, not a market call.

Note also that this would only get things back down to "average". As you might expect, the market spends about half its time below the average valuation level, so bear market bottoms would be expected to be meaningfully lower than that.

Jim