Wednesday 19 October 2011

New Predictions Page with Odds on Golf Predictor

New Predictions Page with Odds
GP video tutorial on this page

Thanks to an excellent user suggestion, a new predictions page has been added to Golf Predictor. This new "Predictions - Tournament Rankings (Odds)" page is identical to the main "Predictions - Tournament Rankings" page except for the last column of the table. The GP Score has been replaced with the approximate unbiased odds for the golfer to win the event. Clicking on the prediction page for any golfer will show the GP Score and approximate odds side by side in the general tab. This new page is accessible from the 'Stats Analysis' menu (second option) in the member section of the site. The screenshot above shows a snippet of the new page for this week's Children's Miracle Network Hospitals Classic. Note that the link to the main predictions page has been renamed to "Predictions" on the same menu.
    This new functionality allows you to easily see if the price offered by your bookmaker for a golfer is fair or too generous/miserly, based on the golfer statistics. Note that the odds on this new page are only the approximate unbiased odds, based on an algorithm that generates them from the GP Score. This algorithm has been calibrated using the pre-event odds and GP Scores for several past tournaments and may need tweaking over the coming months. Note also that I have no prior expertise in odds settings, but have endeavoured to make these odds as accurate as possible.

    As shown above, the book percentage and the overround/underround are also calculated and displayed on the page. The book percentage is the sum of the winning probabilities for each golfer in the event and would add up to 100% in a fair book. The overround* is the positive divergence from a fair book (i.e the amount over 100% that the book percentage is) and is essentially the bookie's profit in the ideal situation of a matched book. Similarly, the underround is the amount under 100% the book percentage is.

    A fair book is very hard to achieve in an event with up to 210 participants! On examination of the book for several tournaments, I found that the bookies didn't even come close (around 160% in most cases)**. Because of this, I decided against adjusting the odds for a fair book, as the resulting prices would be so large as to be practically useless when comparing against your bookie's prices (which are far too low for the more accomplished golfers compared to their mathematical probabilities). Instead, I use the calibration approach outlined above so that value bets might be easier to spot. Depending on the composition of the field (e.g. percentage of no hopers and/or strong performers), the book percentage of my approximate odds can vary from close to fair (i.e. near to 100%) or widely skewed (e.g. 200%). Should enough users prefer the fair book with larger odds (ala Betfair - see below), then I will consider implementing that instead.

    You can set your desired odds format on the member profile page (Member section, "My Golf Predictor - Edit/View Profile" menu option). The options are fractional (e.g. 7/1), decimal (e.g 8.0) or US (e.g. +700). If not set, fractional odds will be used. Like the main predictions page, only subscribers will be able to see the entire field. Non-subscribers will only see the approximate odds for those ranked 11-25.

    Hopefully, this new page will add useful functionality for golf punters. It is available for all tournaments from this week on (week 44, 2011 season - The Castello Masters and the Children's Miracle Network Hospitals Classic). So, sign up today and reap the full benefits of Golf Predictor, the premium professional golf statistics site.

    *Very similar to what is known as the "juice" or the "vig" (short for vigorish) in North America.

    **This is because they have each way markets which can pay out at generous odds. The betting exchange Betfair gets pretty close to a fair book in its winner market. However, its fields seem to be smaller than those used for Golf Predictor (which includes alternates), which is an issue especially for European PGA Tour events. More significantly, the prices for many golfers in the middle of the book are huge compared to bookie prices (the problem I mentioned above for producing a fair book!). This obviously means that Betfair is a far better choice than a bookie for betting on such golfers!

    1 comment:

    Golf Predictor Guru! said...

    This page has been updated with bookie odds for the bigger tournaments. See more on this blog post.