More than once here on the MoS website we’ve looked at the topic of favourite-longshot bias (FLB), which asserts that bookmakers apply a higher profit margin to the prices of underdogs than they do to favourites. In one MoS piece (15 years ago!) I had more of a cursory look and found some evidence for FLB using 2006 to 2008 data, and, in another piece, a few years later I had a more detailed look and found only weak to moderate evidence using opening TAB data from 2006 to 2010.

At this point I think it’s fair to say that the jury is still out on FLB’s existence, and waiting for more convincing evidence either way (and very unhappy at having been sequestered for 13 years in the meantime).

Bookmakers, love them or lose to them, are good at their basic job, which is accurately estimating the probability of outcomes, and they give clues about their probability estimates in the prices they set. The problem is, those clues are cloaked in profit.

There are no doubt a number of viable ways of doing this, but one obvious approach is to fit a logistic equation of the form shown at right.

This provides an S-shaped mapping where estimated win probabilities respond most to changes in expected margins when those margins are near zero. It also ensures that all estimated probabilities lie between 0 and 1, which they must.

I’ve used this form of mapping for many years with values of k in the 0.04 to 0.05 range, and have found it to be very serviceable. I’ve also previously fitted it to bookmaker data and found that it generally provides an excellent fit.

Almost 10 years ago I wrote a blog that, among other things, noted that the score progressions - the goals.behinds numbers at the end of each quarter for both teams - were unique for every game ever played, regardless of the order in which you considered the two teams’ score progressions, home first then away, or away first and then home, choosing at random for every game. At that point, the statement was true for 14,490 games.

It seemed pretty startling then but, as of the end of 2024’s Round 9, the statement is STILL true, and that’s now for 16,487 games. V/AFL games remain as snowflake-like as ever.

With the 2024 Men’s AFL season just weeks away, I thought it timely to look at different perspectives of how teams have historically performed in home and away seasons from one season to the next.