1st Day of November Tendency

I’ve discussed before how the 1st day of the month tends to have a bullish bias.  This has been the case since the late 80s.  (Perhaps due to the rise in popularity of the 401k.)  In July 2009 I looked back to 1987 and broke down the 1st day returns by month

For whatever reason, the 1st trading day of November has shown a positive bias for a bit longer than most months.  Below are the results looking back to 1978.