Rasch Response 3

To continue…

3 Dick: To create an anchor for the scale we group all the scores from a group of students and find their average. To create the scale we use their distribution along a count of correct responses for each item and covert these to different scales, raw scores, percentage correct, percentiles of students, standard deviations, etc.

3. John: I like my multiplication example here because in explaining things we can suggest, let’s say, creating a selection of ten two 2-digit by two 2-digit problems. Then we can do what you just explained for each of the ten problems and for an overall score. Am I understanding correctly?


3. I think so. I am not describing anything new here. I was just describing the traditional method of test calibration in formulating an anchor for a scale, not the Rasch model. I’m not sure I was clear that this was traditional test theory.

The point I was making is that for norm referenced tests the anchor for the scale depends on the group of students tested, i.e., their "norm." That is not a particularly good idea. We must have a scale with an anchor that is free from any group. In fact, we don’t want anything about the scale to depend on the particular group of students or any particular items we use. If the scale is to be objective, it must have its own defined, objective properties that exist independently without being an outgrowth of the performance properties of a certain group of students on a certain group of items.

I’m not sure whether I answered your question since I’m not sure I understood what you were getting at.