[hotShot]

The IMP scale is not linear.
Compare the range for
1 IMP 20-40,
11 IMPs 500-590 or
21 IMPs 2500-2990

So any type of IMP scoring is sensible to those scores close to the datum score. Simulating frequency tables will generate a noise in those scores close to the datum score, while DD results will produce a systematic bias.

I prefer a systematic bias to random noise.

[Jeroen71]

hotShot, on Jan 15 2010, 01:27 PM, said:

The IMP scale is not linear.
Compare the range for
1 IMP 20-40,
11 IMPs 500-590 or
21 IMPs 2500-2990

So any type of IMP scoring is sensible to those scores close to the datum score. Simulating frequency tables will generate a noise in those scores close to the datum score, while DD results will produce a systematic bias.

I prefer a systematic bias to random noise.

DD results do not produce a systematic bias, for most reasonable definitions of systematic bias. It as just as random as the "noise" from the simulated frequency tables.

If my opps bid a ridiculous 7NT that happens to make on 3 finesses and a squeeze, I shrug and move on to the next table. The other pairs in the room are quite likely to have more normal results. However, the DD result is 7NT=, so now instead of, at most, one pair (+their opps) getting a ridiculous score, now everybody in the room will get a ridiculous score. It's not difficult to imagine that all of the pairs that happen to have 7NT on will have a near-zero chance to win the tournament, as they have to make up 34 imps (2 times 17) in perhaps as few as 24 boards.

[Fluffy]

In Spain is becoming popular now playing a 20 VP escale with decimals, where 0 IMP difference is 10-10, but 1 IMP difference is 10.68 vs 9.32 for example, 2 IMP difference is 11.12 ETC... every IMP weights (except those over the maximum).

With butler and computers it seems easy to do the same at datums, so that 10 point difference against datum is sometihgn with decimals and 30 is another thing.

[hotShot]

Jeroen71, on Jan 15 2010, 01:56 PM, said:

DD results do not produce a systematic bias, for most reasonable definitions of systematic bias. It as just as random as the "noise" from the simulated frequency tables.

If my opps bid a ridiculous 7NT that happens to make on 3 finesses and a squeeze, I shrug and move on to the next table. The other pairs in the room are quite likely to have more normal results. However, the DD result is 7NT=, so now instead of, at most, one pair (+their opps) getting a ridiculous score, now everybody in the room will get a ridiculous score. It's not difficult to imagine that all of the pairs that happen to have 7NT on will have a near-zero chance to win the tournament, as they have to make up 34 imps (2 times 17) in perhaps as few as 24 boards.

Of cause you need to score NS and EW separately as you do in an Mitchell-Movement anyway.

Lets calculate that correctly:
Lets assume NS play a NT (vul.) and the DD-Solver can make 13 tricks on "on 3 finesses and a squeeze".
Every reasonable Human player stops in 3,4,5 NT. Those NS pairs that score 600-690 get -17 IMPs a pair making 3NT+4 get 720 will lose only -16IMPs.
So the score of the NS side is "distorted" by 1IMP, this board is not selective at all.
A lucky pair that bids and makes 6NT, will lose only -12 IMPs and gain a 4 IMP advantage over the other pairs on their axis. A lunatic pair that bids 7NT and fails will lose -20 IMPS 3 more then the reasonable player.

The same applies to the EW side.

[helene_t]

hotShot, on Jan 15 2010, 02:37 PM, said:

Of cause you need to score NS and EW separately as you do in an Mitchell-Movement anyway.

I don't see why. Say the EW pairs are generally weaker than the NS pairs. The table results will then on average give higher NS scores than DD. The DD scoring takes care of this while a normal Mitchell tourney does not.

Suppose you have a small tourney with only two pairs! Then all you can do is to compare the table result to some external datum score, day DD or Robot or historical data.

[hotShot]

helene_t, on Jan 15 2010, 02:55 PM, said:

hotShot, on Jan 15 2010, 02:37 PM, said:

Of cause you need to score NS and EW separately as you do in an Mitchell-Movement anyway.

I don't see why.

In the discussed case, the averages of NS and EW have been separated by 34 IMPs as jerome71 mentioned. Each board will alter the averages and although it would average out, if enough boards are considered, in a tourney with a limited number of boards this will not happen.
So the approach to compare NS and EW separately seems fair.

This post has been edited by hotShot: 2010-January-15, 08:06

[helene_t]

Well I just disagree.

Suppose the DD score is 3NT making by NS but most of the NS suckers managed not to bid it, or to go down. This suggests that the NS pairs are worse than the EW pairs and it is only fair that the score reflects that.

Of course it could also be that the 3NT DD result is unrealistic because it requires a lucky split and an anti-percentage line, but the decision to use DD results for the datum score must be motivated by a belief that the DD score is a better datum score than one based on table results would be.

[hotShot]

helene_t, on Jan 15 2010, 03:09 PM, said:

Well I just disagree.

Suppose the DD score is 3NT making by NS but most of the NS suckers managed not to bid it, or to go down. This suggests that the NS pairs are worse than the EW pairs and it is only fair that the score reflects that.

The DD-solver "plays" better than both NS and EW. So the causality you give is distorted. Additionally the DD-solver does not bid, so the optimum playable contract found using the DD-solver is not necessarily biddable. Often the biddable and makable contract will be the same, but if it's not this should not gain to much weight in the players ranking.

Quote

Of course it could also be that the 3NT DD result is unrealistic because it requires a lucky split and an anti-percentage line, but the decision to use DD results for the datum score must be motivated by a belief that the DD score is a better datum score than one based on table results would be.

As usually there are advantages and disadvantages to this approach. One advantage is that the DD-solver is equally strong, not depending of field size or strength, preferred bidding system and pairing. Disadvantages are that that the DD-solver always finds the perfect lead, never misguesses a finesse ...

[pooltuna]

Fluffy, on Jan 15 2010, 03:34 AM, said:

*****

synonyms can do that