After modifying the data file just rerun stdif filename cmd at the DOS prompt

After modifying the data file just rerun stdif

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After modifying the data file, just rerun ‘stdif filename .cmd’ at the DOS prompt to get new DIF indices based on the new criterion scores. You may or may not see a substantial difference in the items being flagged for DIF between the first and second stages. That’s O.K, either way. Note #2 : As you are running STDIF, take the time to look at the filename .LOG file produced by the program every so often. It provides a nice check for you to make sure the program is doing what you want it to do. In the .log file your command file is printed, as well as the line of maximum item scores and switches you put at the top of the data file. It also lets you know 8
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which examinees do not have a proper group identifier for the analysis you’re trying to do and the number of examinees in the reference and focal groups you’ve specified at each of the score levels. Note #3: Keep track (with handwritten notes or otherwise) of which items you are switching off in each analysis, and also the number of items that are “off”. Part III: Summarizing Your Results Item classification is clearly a critical part of these analyses. For each test, note how many items fall into each of three categories after Stage 2. Some rules of thumb for flagging items based on DIF statistics are given below. DIF statistic exceeding ±0.1 DIF statistic between 0.075 and 0.1 (or -0.075 and –0.1) DIF statistics between -0.075 and 0.075 These are items which you will be looking at closer in order to try and infer sources of DIF These items are flagged as potential DIF but are not studied for causes of DIF Items not flagged as favoring one group or another Your reports : There are several tables and figures that you may want to produce for your reports. 1) Descriptive statistics of the test scores in each group (mean, SD, N, coefficient alpha) Table 1. Descriptive Statistics: Grade 4 Test (Number of Items = 42; Maximum Score =72) Subgroup N Mean SD Reliability Reference* 38223 44.31 11.09 .8945 Focal* 36339 47.48 10.79 .8895 Total 74844 45.83 11.07 .8927 *Insert the names of the reference and focal groups you are comparing here (Males and Females, Whites and Blacks, or Whites and Hispanics). 2) Graph of total score distributions : As illustrated below, this is a graph that the relative frequency of reference and focal group examinees at each score point. 9
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0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 Number-Correct Reference Focal 3) Listing of the SDIF and UDIF statistics for stages 1 and 2 (for all items on test) Table 2. Summary of DIF Indices 1 : Grade 4 English Language Arts Item First Stage Second Stage 1 .022 .027 2 -.005 -.002 3 .022 .030 41 -.027 -.023 42 -.029 -.025 1 Items were flagged at the 0.075 level. 4) Presentation of the complete set of DIF indices : This is a graph that visually represents the UDIF values for each item on the test. 10
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Gender DIF Indices for Grade 8 Math Common Test Items MC (1-30) SA (31-34) CR (35-39) -0.150 -0.100 -0.050 0.000 0.050 0.100 0.150 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 Item 5) Summary of DIF Item Statistics : This is a table, as shown below.
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  • Spring '16
  • STDIF

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