I have been doing some analysis regarding games that end in a 1 run decision and thought I might share this with everyone else.
I did the analysis myself using the database at sportsdatabase.com.
Here is what I show: (As you can see there is not a ton of variance from year to year)
All Games
Home Favorites Away Favorites
Year - Games - % Games - %
2005 - 1719 - 69.88% 741 - 30.12%
2006 - 1642 - 66.78% 817 - 33.22%
2007 - 1666 - 67.83% 790 - 32.17%
2008 - 1765 - 71.78% 694 - 28.22%
2009 - 1743 - 70.88% 716 - 29.12%
Total - 8535 - 69.43% 3758 - 30.57%
1 Run Decisions
Home Favorites Away Favorites
Year - Games - % Games - %
2005 - 504 - 29.32% 225 - 30.36%
2006 - 452 - 27.53% 227 - 27.78%
2007 - 464 - 27.85% 218 - 27.59%
2008 - 500 - 28.33% 189 - 27.23%
2009 - 480 - 27.54% 186 - 25.98%
Total - 2400 - 28.12% 1045 - 27.81%
I am left with the conclusion that it is safe to assume that 28% of the games end in a 1 run decision.