2012 Round 1b : He's Done What to the Overround?

Last week didn't really feel like the start of the season to me.

Sure there was a game and goals counted only for six points regardless of their point of origin, but it still felt like an entree - an amuse bouche even. A mismatch that went to script and that, from a statistical point of view, told us little that we didn't already suspect about either of the participants save that, maybe, my Rating the Giants at 900 was a bit harsh. Hardly a game worthy of opening the season.

Not so this week though, where we've an octet of contests and the promise of prolonged suspense about where each game's competition points will be spending the rest of the season. 

The Head-to-Head Tipsters disagree with this assessment, however, voting all but unanimously in most matchups, the lack of unanimity in six of the games coming purely as a result of the underdog's playing at home.

(As usual, images can be clicked to access larger versions - except when I forget to create the thumbnail ...)

In all but the Melbourne v Brisbane game the Away team is the majority favourite, and in all of these games other than the Hawthorn v Collingwood clash it's a 12-1 verdict. For that Hawks v Pies encounter ProPred and WinPred have joined Home Sweet Home in departing from the mainstream opinion.

If you believed all that you'd not hold high hopes for the weekend, but if you instead believed the Margin Predictors you'd feel very differently.

Of the week's eight contests, the Margin Predictors agree with the Head-to-Head Tipsters in seven, but there's far more disagreement amongst them: in four of the games there are four dissenting opinions and in another there's two.

The predicted margins also indicate lesser certainty amongst the Margin Predictors. In total 64 of their 104 margin predictions, or about 60%, are for victories by 2 goals or less and, for six of the games, both the mean and median margin predictions are under 12 points.

Looking purely at the sign of the predicted margins, it's the Head-to-Head Predictors that are the sole dissenting block in four of the games. They favour the home teams in the Tigers over the Blues, in Freo over the Cats, in the Dogs over the Eagles, and in Port over the Saints. For the Hawks v Pies game it's CN1 and CN2 that are the contrarians, and in the Roos v Dons clash it's Bookie_9 that stands alone in support of the Roos.

CN2's faith in the Dees, the only Home team that they're tipping this week, has produced the first and only wager of the round and of the season: 2.5% of the Margin Fund on Melbourne by 1-9 points at $7.50. If the Dees and Lions conspire to produce a result in the required range, the Margin Fund will end the round at $1.1625; otherwise, it'll stand at $0.975.

As I set of for lunch in the afterglow of this wager earlier today I realised what it meant for any of us watching the game this weekend. When we've a head-to-head or line wager we don't care if the result's a blowout, provided the blowout's in the right direction. With a margin wager though, we don't want a lopsided outcome in either direction, but instead need the game to teeter and land within a very narrow range of possibilities. It's the difference between landing a Jumbo jet on a runway and ditching it into the ocean.

The good news - well, fantastic news really - on the wagering front is the dramatic reduction in overround that's evident in the head-to-head and line markets posted today by TAB Sportsbet. Doubtless as a direct consequence of increasing levels of competition in the Australian wagering market, not least from the likes of Betfair, the TAB is now offering us $1.95/$1.95 line markets, and the overround in all the head-to-head markets is of a similar magnitude at around 3%, down from the 6%-7% - and worse - we've endured in seasons past.

To give that a little context to that, it means for example that tipping line results at anything better than 51.3% will now be profitable. Last year, when the line markets were usually $1.90/$1.90 we needed to tip at better than 52.6% to make money, and in the TAB-friendly era of just a few years before that when $1.85/$1.85 markets with 8% overround were the norm, we were facing 54.1% as the hurdle rate. As we've simulated in the past, the difference between 3% and 7% overround is vast.

Let's hope that this isn't just a Round 1 special ...

(One other side issue I should mention is the unusual circumstances of Round 1 wagering. The TAB Sportsbet bookmaker posted markets for all nine games of the Round quite a while back. This included posting markets for the head-to-head outcome and, surprisingly, for a line market. Inevitably, these markets have moved significantly since first they were posted, so much so that the TAB has seen fit to post what they've called Extra Line markets today for most contests, with significantly different points start from the markets as originally framed. These are the markets now priced at $1.95/$1.95 and they're what I've used as input for modelling purposes. The TAB did the same thing last weekend for the GWS v Sydney game but I had then forced the Line Fund algorithm to use the data from the originally posted market. During the week I've relented on this view, which is why you'll notice some very small changes in the Line Fund Probability predictions below.)

To finish, a look at the Probability Predictors' view of the round.

Amongst the Head-to-Head Probability Predictors there's disagreement in five games:

• Head-to-Head Unadjusted disagrees with the Bookie Predictor in favouring the Tigers over the Blues, the Hawks over the Pies, the Dockers over the Cats, the Dogs over the Eagles, and Port over the Saints.
• ProPred and WinPred agree with Head-to-Head Unadjusted in the Hawks v Pies contest

The Line Fund has sided with the Home team in all line markets this week, albeit only very narrowly in the cases of the Dees and the Suns. It's most confident about the line market chances of the Hawks, the Roos and the Tigers.

For those of you who are interested, here are the head-to-head and line markets as at noon today: