Here's an interesting video from Kevin Cook at Zacks.
Doing a search, it looks like Kevin is rehashing Doug Short's article.
The first chart is interesting. It identifies five secular bull markets and four secular bear markets since 1877.
1877-1906 bull (334%)
1906-1921 bear (-69%)
1921-1929 bull (396%)
1929-1932 bear (-81%)
1932-1937 bull (266%) [I call this a bull even though the line is still red on the chart]
1937-1949 bear (-54%)
1949-1968 bull (413%)
1968-1982 bear (-63%)
1982-2000 bull (666%)
2000-2009 bear (-59%)
[from the color on the chart, apparently there was no bull market in 1932-1937 and a secular bear from 1929-1949]
The next chart adds a regression line. The previous bottoms were 33%, 59%, 67%, 59%, 55% below the trend line. The previous tops were 85%, 81%, 12%, 55%, 151% above.
The 2009 bottom was only 11% below trend and we are presently 77% above. The bear case is that there is more room to fall since the previous bears fell much further than 11% below trend.
But even if we're still in a secular bear (like 1929-1949), the market went 266% from the bottom, so we could have more room to run too.