Correction....

Hey Guys!

So my last blogpost about what the 1st set price should be turned out to be very interesting. I was wrong in my calculations, they where no good. But I love being wrong cause then I have a chance to get it right! =)

Thanks to Rico for his input but also the rest of you guys making it a good discussion.

This is Rico's explanation and it might seem a bit complexed but nothing overwhelming. This is how you should do it!

"Let's say we know match odds for player A are 1.6 and we want to find set odds (assuming these stay constant during the match). 

There are three ways for player A to win, he can win by 2-0 or by 2-1 after winning set 1 and losing set 1. Let's say his odds to win a set are x, then his chance to win by 2-0 is x^2. His chance to win 2-1 after winning set 1 are x*x*(1-x)=x^2-x^3 and this is the same for winning 2-1 after losing set 1. 

We can sum these three chances and get to the total chance of 3*x^2-2*x^3 . We now have to find the value of x where this sum is equal to 1.6 and by using the solver in Excel you can fnd that x=58.75% ."

Spot on. Im not a excel master at all. It took me sometime to figure it out but if I can do it. Everyone could do it using google to search for excel help.

One thing to keep in mind is that these 1st set theoretical prices is just viable if the starting price odds was correct from the start (that the market had valued the match correctly from the start). Also, a lot of stuff happens during a set and market will adjust and correct itself a lot and there for the set price usually isn't what the calculated theoretical price is when the first set is finished.

Stay Sharp!

/Sammy

What "should" the set price be?

Hello! First of all I'd like to thank you guys for the kind words I have received about the Podcast. It was good to hear that you found it interesting. Cheers!

So I got a question on twitter regarding an old blogpost from last year about calculating what the odds should be after first set and how to calculate it. http://betfairtennistrader.blogspot.co.uk/2013/12/question-from-reader.html

The question I got was instead of having the pre-match odds @ 2.00 for both players. "Lasse" wanted to know how the math is done for a 1.60-2.67 match. So I had a look at the card for the day to have an example. Tonight David Goffin plays versus Jerzy Janowicz. The odds on betfair when I write this is now @ 1.65-2.54 which is close to what we want to calculate here. To make it easy we use "Lasse's" prices.

So this is basic probability calculations and in theory what the price "should" be after first set. You have always consider if the match was rightfully priced from the beginning and what is happening during the first set.

Anyways, here goes...

Lets start to look at what the market is giving us for probability for each player winning the match.

David Goffin (favorite): 1.60 -> 1/1.60= 63% (0.63) - So the favorite is priced to have a 63% chance of winning the match. Now its easy to calculate the chances for the underdog.

Jerzy Janowicz (underdog): 100%-63% = 37% (0.37)

So we assume that each player have the same chance of winning a set, and now that we have probabilities for winning the match its pretty easy to get the theoretical set prices for both players. This is probably where the "mindf*ck" part comes into it but its easy when you know how to do it. Ill skip the probability mumbojumbo and just go straight into how to calculate it.

Lets assume that Goffin wins first set. To calculate his set price, we calculate Janowicz chances of winning the match first from being behind a set. This means what are Janowicz chances of winning two straight sets.

37%*37% (0.37*0.37) = 0.1367 = 13.7%

If we subtract 13.7% from 100% -> 86.3% (0.863) (This is Goffins chance of winning the match after he won first set)

And to get this into odds form -> 1/0.863 = 1.16

Lets see if you can get Jerzy Janowicz theoretical set prices if he wins first set! I think you can do it! =)

Stay Sharp!

/Sammy