Stats Busters: Are Melbourne AFLW teams overrated?

The AFLW certainly isn't one of the biggest betting sports in Australia, but the attention to it does seem to be growing this year, and one of the theories going around in betting circles and on social media has been to avoid betting on the Melbourne teams. In this edition of Stats Busters, we take a look at why people might think that's the case, an approach for investigating it, and whether or not it's true.

The Logic

The AFL is undeniably a Melbourne-centric sport, and AFLW is no different. Not only are half of the teams (4/8) Melbourne based, but so is most of the media, and - arguably - most of the punters. So, just as the logic goes that LA teams are usually underpriced in Vegas, because punters from LA who can't gamble online or locally (at least legally) make the trek to Vegas and support their local team, it would make sense if the bookies shaded the line against the Melbourne teams, given punters may wager on them anyway.

The Scientific-y Method

Applying science to AFLW comes with a massive caveat -- there just aren't many games. We could apply this to the wider AFL - and we may do so in the future - but for now let's just accept the limitations and get on with it...

Melbourne teams W/L percentage split

With our database of AFLW results, we first coded the games to select those where a Melbourne team took on an interstate team, whether played in Melbourne or out of state. We then looked at the closing bookmakers price, as the best estimate of the market. Across the 25 games (excluding 1 tie), the Melbourne teams had average odds of $1.62 (transformed to a 100% market). Thus, we'd expect them to win about 61.6% of the time. Across the 25 games, they actually won 48%.

The other way to look at this is what would have happened if you bet on each Melbourne team to win? The answer is: nothing good. Wagering $100 on each team would have meant you spent $2500, for a loss of $482 (-19.3%):
Now, that being said, I'm not ready to call this one "Confirmed". Why? Well if you'd just bet every favourite, you'd have a pretty similar looking graph. Indeed, you would have made almost 40% betting on every AFLW underdog since the start of the league. That means we have to question whether the betting market gives us an effective estimate of how often they should have won.

Result

All that being said then, what's the conclusion? Well, we can't say for sure that Melbourne teams are being systematically overpriced, as the logic would suggest. But, we certainly can't refute that either. So, for now, and until we have more data, we'll call this one...

SI Verdict: Plausible