How-to-use BRidgeBRowser
DAY SEVEN
Question 6:

How many points should you have to bid 6NT, assuming no five card suits or singletons?
 
Day 1 Day 2 Day 3 Day 4 Day 5
Day 6

We are going to start today with a little bit of insight. Why is it necessary to perform some of the steps and why do they differ from problem to problem?

The answer is indexing. If we had an infinitely powerful computer with a huge disk and infinite amounts of time we could make indexes on every conceivable property of a bridge hand. Some of these indexes take days to build. Sigh.

However as bridge players you all know that there are a LOT of bridge hands, and the indexes that it is possible to prepare are essentially only the ones that we think common questions might be asked on. Then we combine the commonly-asked questions into something meaningful to get a result in a short enough time that we don't spend an eternity getting it.

For example, it's relatively easy to look up all the hands of one player in a given data file. Just fire up the wizard (on the Help menu of the BRBR application), and fill in the parameters. The wizard simply fills out the box on the "players" tab - which is of course far more complex than searching for a single player - and sets going a player search.

On the other hand, if you wanted to look up all the hands played by player X in 6NT, you might go about it one of several ways:

a. Look through all of the data in a linear fashion, crosschecking for player X and 6NT contracts (auxiliary terms for the latter two)

b. Look through all player X's hands, keeping only those records with 6NT as the contract

c. Look through all 6NT hands keeping only hands involving player X. Minor problem, we don't have a contract index available.

d. Look for all hands with 30+ points (create a board index with this as the primary term) held by one side or the other, and crosscheck for 6NT contracts and Player X.

e. Look for bidding sequences where the last indexed bid is higher than 4S. Since we don't index past the first 8 bids, this is not a very good test. (it works in reverse for finding unusual low-level sequences though)

It turns out that d. is much the fastest (because there are only 1/50 the number of boards compared to the number of hand records) for many types of question involving shape. This is how we will search for 6NT vs points. We will look for hands held by the dealer and partner totalling a specific point count, and shapes 4333 and 4432. We will only keep those played in 6NT. The only drawback is that because we start every time with the BOARD, we cannot do bidding-dependent searches, such as all hands where someone opens 1NT regardless of seat. You have to search one seat at a time. Today we can do 1 (dealer)+3, the 2+4 is left as an exercise for the reader.
 
1. Fire up BRBR Online. The latest version is 2.3A-h-4
2. Select S(can R(eset All (only need to do this once, just make sure you haven't restricted all your searches on some previous visit).
3. From the F(ile menu select "choose dataset". There are two new files, 2001-data.brd, and 2002+data.brd. These omnibus compilations are of all the hands before and after Dec 30, 2001 respectively. (you can click on the .PLY file too with the same result). We need to do this because there are not enough hands in a single chunk of 6 months that you have used up until now. Fear not, as the board index does reduce the work drastically provided you follow the instructions below. The newly opened file should display its credentials at the top of the page, including filename and number of records.
4. Click on the tab about halfway down, BELOW "BRidgeBRowser (tm)" which says "Brd Shape/HCP". Click "Clear Terms".
5. In the Brd Shape/HCP tab, click on the following terms, in order:

a. HCP Team - Dealer
b. Shape - Dealer
c. Shape - 3rd pos.

Over in the terms, set the initial value and limits of term 1 to 30 HCP.
Set the initial value and limit of term 2 (shape 1) to 4333 and 4432 respectively.
Set the initial value and limit of term 3 (shape 3) to 4333 and 4432 respectively.

The result should look like this:

 
6.  Click on the tab marked Bid Analysis, check the "Enable as auxiliary term" box. 
7. Click on Contract/Lead, and click on the radio button marked "Specified". Clear all contracts by clicking on the TOP LEFT square in the grid. Now set (only) 6NT and 7NT by clicking those two squares once. The result should be:

Click on the "enable as auxiliary term" for the contracts tab.
 
10. Go back to Brd Shape/HCP tab, and press "Search". Go to watch the output on the bid analysis tab, which you remembered to turn on. Move the slider to CtrOS to get the averages and frequencies for the final contract.

When it is done, there should be a beep, and you can see the result. As before you can export the tables (including Standard Errors) to a spreadsheet. 
 
What I did was to break down the results into a number of sub-searches, because I noticed that the averages always improved as the search progressed. Since results for a given point count are returned in the order of the "shape" term, all the hands where both players have 4333 come first, and all the hands where both have 4432 come last. In between are the hands where one player had 4333 and the other had 4432.

Then I repeated the whole thing (4 searches) for each point count holding, 30 through 35.

I made these results into a spreadsheet, which you can download here if you don't want to do it yourself. It looks like this:
 


 
RESULTS

1. Conventional wisdom has it that 33 points are needed to bid slam. This data says that is only true only when you have 4333 in both hands. With two extra four-card suits you only need 32. And on IMPS you should always bid on 32 anyway with only 1 4432 hand (of the partnership).

2. Past 34 points, the values start to diminish, because now some hands are making 7NT. 
 

 
NOTES:
1. You should (always) get the latest client. It last changed on 22 February. You will be locked out unless you have a recent one. No more Mr. Nice Guy, we had some crashes from folks using a very old client. I'll try and automate this soon.

that address again:

http://www.microtopia.net/bridge/downloads/online.exe

2. Remember to try 2 + 4 seats!