Advice

How To Make A Power Rating

There’s no doubt that ratings are a great way for you to analyse a race. In fact, they’re probably one of the best ways.

But I’m a self-admitted ratings fanatic!

So with the admission that I love ratings. The question is… is there anything better than a rating?

And the answer is yes.

A power rating

Power ratings are combinations of other ratings with the aim to provide a single number that effectively takes into account a range of different factors of a horse’s performance.

The key word in the above paragraph is “effectively”.

It’s easy to just combine a bunch of ratings together and call it a power rating. But to make one that assigns the right level of importance to the different ratings that are being combined is much harder.

The two big issues in making a power rating are:

  1. The ratings are measured on different scales
  2. How much weight to give each rating

Which is why today I want to show you a good way to solve both of these issues quickly and simply.

It’s often over-looked that ratings are measured on different scales.

Often one rating will be on a scale of 0 to 100 and another on a scale of -100 to 100. Some may be on a scale of 0 to 1 and use decimal places.

There are, of course, almost limitless possible scales that a rating could be measured on.

But even if you have two ratings that are measured on a scale of 0 to 100, they may not actually be on the same scale fully because 1 point for each of the ratings may have more or less impact than the other rating.

And if it does that means that the rating can’t be considered to be on the same scale.

In order to get around this I prefer to use Impact Value (IV’s) or Pool Impact Values (PIV’s). Pool Impact Values are also often known as A/E in the UK.

If you’re not sure what impact value is then you can get more information at:

http://www.raceadvisor.co.uk/?s=impact+values

But the quick overview is that if a horse has an impact value of 1.20 for a particular rating then it is winning 20% more often than would be expected.

By converting a horses ratings into IV’s we have solved the first issue of building a power rating.

All IV’s are measured on the same scale.

Which brings us to the next problem, of determining the importance of a rating and how much weight should be assigned to it when combining all the ratings together.

In order to determine the importance we’re going to use an approach that required trial and error.

It’s possible to use all sorts of statistical approaches, all of which are quite complicated.

A systematic trial and error approach can be done by anyone with a simple spreadsheet, all you need is the patience to go through it and get it right.

Start by assigning a weight of 1 to each of your ratings. That means we simply multiply a horses IV’s together to get a final rating.

Take the top three rated and see how often they win or come within one length of the winner.

I prefer to use one length of the winner because my goal is to get as many of my top three selection contending as possible.

This now gives you a baseline to measure against.

Take one rating and give it a weighting of 2, that means you multiple a horses IV for this rating by 2 before combining it with the others.

Analyse your new top three rated horses and see if the performance has improved or declined and by how much.

Now change this ratings weighting back to 1 and increase the next ratings weighting to two.

Repeat the process.

By the time you have done this for all the ratings you will have a good idea of which one should be the most strongly weighted, second most strongly rated etc…

Now it’s time to apply your weighting to each of the ratings using this knowledge and you have created your power rating.

This approach to weighting is a rough and ready approach that is not going to be perfectly statistically accurate.

But…

It will be accurate enough to highlight the three strongest runners in each race so that you can determine how you want to bet on them.

Michael Wilding

Michael started the Race Advisor in 2009 to help punters improve their betting profits and think outside the box with their betting strategies. To date he has written over 450 articles on the site and recently started UK Racing News which has become a leading news site for horse racing in the UK and IRE. Check out my personal blog or my Google+

4 Comments

  1. Hi Michael,

    Thank you for another interesting article.

    I’m of to Punchestown for the rest of the week, but I have some questions for you,

    i.e.
    How would you go about sorting out the three best horses for consideration in today’s 5:30 at Punchestown.
    Starting with Racing Post Ratings, Topspeed, Postdata, Betting Forecast and Form Study etc.

    Having read the above along with the two articles from the link above I’m none the wiser as to how I can best utilize everything in order to to be able to select the best three horses in today’s race.

    I’ve copied the answer you gave re PIV below.

    I don’t have a problem with the figures, but it doesn’t help me to select the the best three horses for consideration in today’s race.

    I don’t want to appear totally stupid but maybe a further article as to how you would go about selecting the three best horses using the methods from your posts.

    Kindest regards

    Ramsey

    RA Admin February 20, 2012 at 10:20 am
    No problem Jeff. If we have 5 selections with odds of…

    5
    12
    3.75
    2.50
    6.2

    We then do the sum of 1 / Odds for each of these…

    1 / 5 = 0.2
    1 / 12 = 0.083
    1 / 3.75 = 0.27
    1 / 2.50 = 0.4
    1 / 6.2 = 0.16
    Ll
    We sum together the results of each of these calculations…

    0.2 + 0.083 + 0.27 + 0.4 + 0.16 = 1.113

    This means that we would have expected to have had 1.113 expected winners from these 5 runners.

    If we actually had 3 winners then we would now do the sum…
    L
    3 / 1.13 = 2.65pl

    The PIV for these selections is 2.65. Obviously you would need far more selections to get an accurate figure but I hope that clears the process up.

  2. Hi Michael

    Another great article is there programs out there that can do the initial calculations for you

    as my top ranked maybe IV 1.2 but you need to get the PIV/IV for all your lower ranks from historic data

    which could take time

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