Ben Stein co-wrote an interesting book Yes, You Can Time The Market about buying an index fund when its selling at a discount as determined by different metrics. For example, the market might be a bargain if the current avg. PE ratio of the S&P 500 was below the long term PE average. And current share price significantly below a long term average, etc.

Look at that 50 day moving average relative to today's price. How many investors would like to buy something at 80 percent off the fifty day moving average and that company has a good chance of being profitable by the end of the year? No one? Crickets? They'd rather trade moving average crossovers for a buck here, a buck there, a baloney sandwich here, bag o' chips there? As a long I don't know what good a 10 or 20 day MA does for me.

Of course, disclaimer, everyone should do their own DD...
Cheers