Negative,
These are the avg odds on the favorite for the years:
avg smaller odds
2011 1.4416368078
2010 1.4468241578
2009 1.3874011706
2008 1.4382330472
2007 1.4656253219
This is the distance to 2 for the favorite squared
avg (2-smaller odds)^2
2011 0.3728082248
2010 0.3654913837
2009 0.4282047519
2008 0.3769435009
2007 0.4215296897
Looks like games are balanced out.
I also mistakenly used the short version for vig free, here is updated with the root:
Variance Std
2011 0.1961877702 0.4429308864
2010 0.1935183146 0.4399071659
2009 0.1948075505 0.4413700834
2008 0.1918060137 0.4379566345
2007 0.1801504604 0.4244413509
arith mean: 0.1912552205 0.4373273608
Over PM someone asked for the data source,
http://www.tennis-data.co.uk/alldata.php.
Data comes without pinnacle open odds, I will use the log scoring as proposed tommorw and post results, but so far it looks like for backtesting purposes WTA data is valid for the last 5 years.