Best 10 years in returns term for S&P from 1926 to 2014
Worst 10 years in returns term for S&P from 1926 to 2114
2014 will be around 12% year based on how we close. You can see the database for 1926 to 2014 here.
Breadth statistics are valuable because they give some of the best indications about the health of the liquidity that is available to the stock market. A small amount of money can be employed to make a handful of stocks go up or down, and if they are the right stocks then even the major market indices can be moved. But to affect the breadth numbers, which measure all of the stocks on the exchange, requires major changes in the liquidity picture. The available money has to be so plentiful that it can be spread far and wide in order to make the majority of stocks close higher, and especially so in order for the market to show positive breadth for several days.
From the McClellan paper