Enhance an IbreaksMH chart

Hunting for pictures of DIF, differential item functioning?


Use the IbreaksMH tables. Scroll to an item of interest; select that part of the scores range of interest, and hunt away.


For example, we might look further into the IbreaksMH table for item I35.




The chart below was made by selecting I35's two diff rows, starting at a score level of 8, extending out to a score level of 36.  Then the "Line" option on Lertap's Excel 2007 ribbon tab was used (you don't have to use that option: <Alt+F1> is a shortcut which accomplishes the same thing -- with the <Alt> held down, press on the <F1> key).




What have we here? A conventional Excel Line chart, with two "series". The y-axis plots over proportion correct. The x-axis, at this point, is just indicating a sequential data point number. Things could be improved, for sure.


The "Enhance M-H charts" option on the Run menu can help out.




With an IbreaksMH chart still selected, click on the Enhance option. The original chart is improved by adding a title, I35, correct legend labels, Nat. (r) and Ing. (f), and dinkum score values along the x-axis. See here:




The chart for I35 reflects an item that meets the ETS criteria for C (large).  There's quite a range of scores where the Nat. group consistently out-performed the Ing. group.  This is a picture of DIF.




This chart, for item I1, reflects no DIF, ETS level A (neg.).


If you go though an IbreaksMH report, making plots such as these, remember that you can move them to another worksheet quite easily.  See the Ibreaks charts topic.


Related tidbits:


For other pictures of DIF, see, for example, Figure 4.4 in Camilli & Shepard (1994), and FIGs. 3.1 and 3.3 in Dorans & Holland (1993).  (Refer to: http://www.larrynelsonstuff.com/References.htm.)