This chart is from

So if we use the 1974 bear market as comparison to our market, we nee our trailing PE ratio to be around 8 before the bottom is found.
The same thing can be found here.

Currently I estimate that with S&P 500 at 900, the trailing PE is 17.4 (SPY PE shows 14ish, but I think these are a little old). That means we need a 50% price hair cut to return to 1974 lows. Going forward we expect earnings to drop more, requiring an an even bigger drop in price to bring us to a low PE.
So next time you hear that the PE ratios are attractive here, remember this.