Is [The] Santa Claus [Rally] Real?

The end of this week will bring the end of November, and with that there is the usual seasonal talk about a Santa Claus rally in the stock market.  The logic goes that stocks usually rally between Thanksgiving and Christmas, but much like with Kris Kringle himself, it's fair to ask the question: does the Santa Claus rally really exist?

Looking at the historical data, since 1957 December has been a positive month on average for equities.  In the past 5 years it has been especially good--powered by a nearly 11% gain in 2008 and 4% gain in 2010.  Below is the average path that the S&P 500 takes during December.  It demonstrates some Christmas magic may indeed exist--the path is even strangely sleigh like...