Author: Stephen A. Boak
Date: 18:25:59 12/28/04
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On December 28, 2004 at 20:54:45, William Penn wrote: >Statistics errors in opening books created with Shredder8/Fritz-GUI >------------------------------------------------------------------- > >I have been creating opening books for quite awhile with the Shredder 8 >CB/Fritz-GUI. [I'm talking about the same GUI that comes with Fritz 8, Junior 8, >etc. - not the "Classic" Shredder GUI. Too bad such ambiguities exist, but >hopefully that is clear enough.] > >The procedure (from the chessboard window in the GUI) is: >1) File menu, New, Openings book... (creates a new opening book) >2) Edit menu, Openings Book, Import Games... (imports games from any desired >database) > >The resulting opening book can be displayed in the Book Pane. That is available >by default as one of the tabs in the Notation pane, along with the Notation and >Scoresheet tabs. Or it can be displayed separately by selecting "Extra Book >Pane" from the Window menu, Panes... > >For any given position on the chessboard, the opening book shows the number of >games, percentage scored, average rating, performance, and probabilities - >overall, and for each of the possible moves in the position from the database >involved. A histogram (bar graph) can also be displayed at the bottom of the >Book Pane with the number of white wins, draws, black wins, percentages, etc. > >Much to my dismay, I have just discovered that the data and statistics shown are >inaccurate. There must be a bug somewhere. > >While the total number of games in a given position appears to be correct in all >cases, the other statistics & data for the variations is incorrect. For example >there may actually only be one (1) game in the database for a particular move >from the position, but the Book Pane may say that there are 3 games, or 5 games, >etc. with corresponding incorrect statistics. Search of the database involved >for that position proves that the displayed statistics are incorrect, which is >easy to do when only a few games are involved. > >This error always displays more games than actually exist in the database. >Exactly where the "extra" games come from is a mystery, because they do not >exist in the database. It could be some kind of tree-building error when the >games are imported. Or it could be an error in how the data is displayed (more >of a GUI-based error). I don't know which. > >I also don't know if the error relates to the Length designated when importing >games. That dialog box which appears asks you to select an Absolute length or an >ECO-relative length of 1-100. This determines how big the tree is. The larger >the Length selected, then the bigger (more MB or GB) the resulting opening book. >I usually choose a Length in the range of 15-35, depending on the size of the >database. > >I also don't know if the error relates to the size of the database involved. >Most of my databases are large, the largest over 3,000,000 games. Or perhaps >there is some limit on the size of the resulting book files, but I don't know. > >At this point, I also don't know exactly how bad the error is. If it's only a >handful of games, it wouldn't matter very much when the sample of games in a >given position is large. > >The uncertainties involved makes the resulting statistics practically worthless, >pending further research. Too bad, because it could be quite valuable if >accurate based on the database involved. > >At this point, I'm not aware of any way to avoid this bug. Does anyone know how >it can be avoided? > >My apology for saying "I don't know" so often, but alas there is no detailed >documentation or instructions for these operations insofar as I'm aware. You >just have to discover them on your own, then try to get lucky, I guess. Alas >that is typical of Chessbase documentation. They assume you already know >everything. >WP I have detected similar puzzles in the past. Some thoughts (ideas only): 1. Transpositions may mean the position arrived at after making the displayed tree move was reached from different prior positions. Thus a search from the current position may only show one instance. 2. Some transpositions may be included only in the notes within a game, but not with a separately saved database game entry. 3. Reversed color openings may be included in the statistics, but a search may not find them, even if "equivalent". I suppose a test, creating a small database and corresponding tree, *may* show something, but then the problem may be hard to replicate. Let us know if you learn anything more. Regards, --Steve
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