Stat 778 - Spring 2006 - BILOG Templates

The Basics of BILOG

The Basics of BILOG:

The basic example for BILOG will use the data set mdatabid.dat which is simply the math data used in the R templates with a 5 digit id added.

When starting BILOG-MG for the first time you will be confronted with a gray screen. Your first goal is to construct the appropriate .BLM file that will contain the commands for analyzing the data. If you already have a file that is similar to the one you want, you could choose FILE > OPEN and open that file to edit it. If you want to start from scratch, you can choose FILE > NEW and choose the directory you want to save the .BLM file in.

The lines below are a sample .BLM file for analyzing the math data set (saved on my Z drive). 

Sample Bilog Analysis
of mdatabid.dat
>COMMENT
This is the same data set analyzed in the R templates
>GLOBAL DFName = 'Z:\mdatabid.dat', 
        NPArm = 3; 
>LENGTH NITems = (32);
>INPUT NTOtal = 32, 
       NIDchar = 5;
>ITEMS ;
>TEST1 TNAme = 'TEST0001', 
       INUmber = (1(1)32);
(5A1, 1X, 32A1)
>CALIB NQPt = 40, 
       CYCles = 40, 
       NEWton = 5, 
       CRIt = 0.0010, 
       ACCel = 1.0000, 
       TPRior, 
       GPRior;
>SCORE NQPt = (40);

To try this example, first save the math data set on your computer. Choose File > New and select the directory you want the analysis to be saved in. For the File name: use something like mathexamp. Now copy and paste the above code into the main window. The only change you need to make is that the name of the file on the DFName has to match where you saved the data set and what you called it.

If you go to Setup > General you will notice that everything is either blank or set to 1. In order to get the options filled in, you need to choose File > Save twice. (Apparently there is some sort of bug that makes this necessary). You can then run the .BLM command file by choosing Run > Stats, Calibration and Scoring. You should see three black text boxes appear on the screen with values flashing quickly across them, and then vanishing. A box labeled Run Successful should appear and you can hit OK. This will have created three output files in the directory where you wanted the analysis: mathexamp.PH1, mathexamp.PH2, and mathexamp.PH3 in addition to the mathexamp.BLM file you saved there. As discussed in class, these files contain the classic statistics, IRT item parameter estimates, and examinee ability estimates respectively. You can also see the output by using the Output menu option. The options for seeing or moving back and forth between the various windows can be found under the Window menu.

To modify this to analyze another data set, begin by choosing File > Save As and choosing a name for the new BLM file. You now have two choices:

  • Modify the code in the window using the seven steps below and hit save twice
    1. Change the top two lines to have the title you want
    2. Change the line below COMMENT so that it is appropriate (you can have a large number of lines if you have many comments)
    3. Change the location of the file on the GLOBAL line
    4. Change the length of the exam on the LENGTH line
    5. Make sure the number of items and length of the id are correct in the INPUT section
    6. Make sure the 32 on the INUmber line is changed to the number of items you have
    7. Make sure the 5 on the next line is the length of the ID characters and the 32 is the number of items.
  • Or, use the menus to make modifications, choose Run > Build Syntax and then save
    1. In Setup > General change the title and comments to be appropriate, adjust the number of items, and hit ok
    2. In Setup > Item Analysis change the subtest length to the number of items and hit ok
    3. In Data > Examinee Data > Data File put the correct data set in (you can hit Show Data if you want), adjust the column setting for the response string, hit Set Format, and hit OK. (You can go to the Enter Data tab and choose open if you want to make sure it worked ok.)
    4. Choose Build Syntax and File > Save
    5. Check to see if the NQPt=40 line has vanished. If it did, go to Setup > Item Analysis > Advanced to make that value 40 and hit ok. Then repeat step 4.

    Once the .BLM file has been updated, simply choose Run > Stats, Calibration and Scoring.

    An additional option you may wish to go back and shoose is to check the Score Output option under the Save menu. This will produce a file ending in .SCO that has the examinee scores, but not a lot of the extraneous information. When you hit Run > Build Syntax notice that this adds the line > SAVE SCOre='xxx.SCO'; to the .BLM code (the xxx is the file name and remember to choose save).