Here's How Devastating a Bear Market Can Be

You don't have to be Chicken Little to think the sky could be falling.

Consider all the dire economic headlines lately:

* China's growth has hit the skids and the world's second-largest economy may be in for a "hard landing."
* America itself may be at risk of slipping into a recession.
* Oil prices have collapsed, hinting at an economy headed in reverse.
* A strong dollar has waylaid corporate profit growth.
* Industrial production is on the decline.

All of these headwinds have contributed to the terrible start for stocks this year, with the S&P 500 dropping 8% as of Monday's close. Stocks have declined almost 13% since last May's highs, which means we are firmly entrenched in a stock market "correction." Smart minds have begun to wonder whether our nearly seven-year bull market is coming to an end.

So much has happened since the last bear market ended in March 2009 — Jack Dorsey hadn't yet come back to run Twitter — that it's helpful to refresh your memory with a bit of context:

Duration
There have been 12 bear markets (roughly defined as a loss of 20%) since 1946 and, on average, stocks took 14 months to drop from the high point to the absolute bottom, according to S&P Capital IQ's Sam Stovall. If we assume we're entering a typical bear market and believe the end of May 2015 was the peak, that means we could hit our trough at the start of September 2016. (Incidentally, some kind of election takes place later in the fall.)

Severity
The average post-World War II bear saw stock prices decline by one-third, Stovall notes. That means the S&P 500 could drop to about the 1,427 level (it closed Monday at 1,877), which is about where the index was in the middle of December 2012.

Recovery Time
It takes more than two years (25 months on average) to claw back the losses, or about when the next non-presidential congressional elections will take place in 2018. That's about a 40-month sidetrack.

And things could be worse — the last two bear markets (caused by the dot-com bursting bubble and the housing crisis) took 56 and 49 months to break-even, respectively.

Breadth
Just like a good horror film, there's really no place for investors to hide. In the last three bears (1990, 2000 and 2007), both growth- and value-oriented shares dropped big, and every sector except two (consumer staples in 2000 and utilities in 1990) fell. So if the bear comes, you're going to be mauled for what seems like a very long time.

Putting Things in Perspective
It is worth mentioning, though, that further declines aren't written in stone even though this has been the worst January in history. As Money's Paul Lim points out, of the previous five worst Januaries for stocks, "only one of those episodes — 2008 — turned out to be a down year." If the European Central Bank continues an easy policy, and the Fed pushes back expected interest rate increases, or some other unknown events transpire, investors may feel more optimistic and buy.

But if we've already fallen off the cliff, remember, this too shall pass. Experienced long term investors should know by now that you only sell when you can't imagine the market ever going down, not the other way around.