I have thought in the recent past that oddsmakers are getting better. Mostly, I have used anecdotal data to prove this. I have read many comments from sports bettors who have been around for some time say that sports betting is tougher than ever to beat. Usually, one of my strengths is that rarely take statements like this at face value. I am pretty good at finding out for myself if something is true or not, and not just taking someone elses word for it. I failed in this instance.
I undertook a quick test to determine if the lines by oddsmakers are getting better and the answer is clearly no.
Unfortunately, those lines are not getting any worse, but sports betting is just as beatable as ever. I looked at results from the last 20 seasons in the NFL, and the last 10 seasons of the NBA, and determined how far from the actual results did the lines come. In other words, if a 5-point favorite won the game by 12 points, the distance between the two is 7 points.
That would be the same if a 5-point favorite lost by 2 points. I then averaged the differences for each season. As you will see, there is no appreciable difference over time. Oddsmakers are just as good (or just as bad) as they have been in recent history.
Here are the results:
NFL Avg. Diff