In Backgammon, why is the match length almost always odd? And why are 9-point matches twelve times less popular than 7-point matches?

I was wondering what was the ideal match length, and I came across those statistics:

Matchlength : Total Matches
1 : 350
2 : 59
3 : 634
4 : 12
5 : 1184
6 : 1
7 : 492
8 : 1
9 : 42
11 : 31
Total : 2806

The match length is almost always odd. Why is that? What's wrong with an even match length?

Also, 9-point matches are 12 times less popular than 7-point matches (a difference way too big to be explained by the fact that 9-point matches take slightly more time than 7-point matches). So why are 9-point matches relatively rare?

• Maybe this is some Backgammon terminology that I don't know, but is the "matchlength" the number of games per match? If so, then an odd number seems obvious; because with an even number, you could end with a tie. 9 and 11 would be less common simply because that's a large number of games to play. Mar 8 '15 at 19:34
• In K-O tournament formats, later matches are typically longer than earlier matches. In Swiss tournament formats a primary goal is to maximize number of matches, and thus number of opponents, so individual matches are shorter. Mar 8 '15 at 20:25
• @GendoIkari: Check out the Doubling Cube in Backgammon - It is unusual for an individual game to be worth only 1 stake by the time it terminates; more normally the cube will have been turned and accepted once or twice for a stake of 2 or 4 for the game. Seven-point matches can usually be concluded in an hour. Mar 8 '15 at 20:29
• @GendoIkari: Also check out this answer for an example of why well-timed doubles are usually accepted rather than declined: boardgames.stackexchange.com/questions/23237/… Mar 8 '15 at 20:33
• @freevkd It's the number of points required to win the match (gammons, backgammons and doubling cube included). Mar 9 '15 at 10:23

1 Answer

Largely it's by convention, but the historic cause is the way optimal doubling cube strategy varies with the match length. In the most easy case, in a 2-point match it can barely be wrong to double as soon as you are ahead, and far too easy to leave doubling too late - which means the match becomes a single game the vast majority of the time. In which case you might as well play a 1-pointer. The other small even match lengths suffer similar oddities, but less pronounced as the length increases. Odd match lengths tend to have more "normal" doubling strategy in the early stages.

On at least one server I play on, 2-pointers are frowned on because they are perceived as a way of playing a 1-pointer for double the ratings value...