At the end of its Round 20 the 2012 season remains notable not just for the predictability of game outcomes but also for the relatively infrequency with which teams that have lead by more than a few points have ultimately relinquished that lead.
Here's a table comparing this year to last in terms of the fate of teams leading by various amounts at each change.
As an aid to reading this table, consider the row labelled "1 to 5 points" in the End of Quarter 1 Summary. It tells us that there have been 35 games where such a lead has been established by the end of the 1st quarter and that the team which held this lead went on to win 20 of those 35 contest, which is 57%. The "Cum %" column tells us that teams which have led by this margin or more at quarter-time (ie teams that have lead at all) have gone on to win 77% of games. The equivalent percentages for 2011 are 54% and 64% respectively.
For me, probably the most telling lines of these tables are those that record the cumulative performances of teams that led by 6 points or more at quarter ends. Teams that led by this margin or more at quarter-time have won 83% of the time this season compared to just 67% of the time in 2011; teams that have held similar leads at half-time this year have won 90% of the time compared to 76% in 2011, and teams that have enjoyed a single goal lead or more at three-quarter time have gone on to win 93% of the time this year compared to 91% of the time in 2011. You just don't want your team to be trailing at any point in a game this year.
We can even relax the need for a team to be in front by at least a goal and note that teams that led by any amount at quarter-time have won 77% of contests this season (vs 64% last season), teams that led by any amount at half-time have won 85% of contests this season (vs 73% last season), and that teams that led by any amount at three-quarter time have won 88% of contests this year (vs 84% last season). So much for the glorious unpredictability of sports.