3. Creating Parallel Forms Using IRTTo construct two parallel forms using IRT, a test developer can follow a procedure similar to the one for creating a single form. Item parameters and item information functions are examined to create TCCs and TIFs that maximize measurement precision in a specific ability range. Forms are judged to be parallel if they have nearly identical (overlapping) TCCs and TIFs. To illustrate how to create multiple parallel forms of a test with desired psychometric properties, we designed two Excel workbooks that can be used to construct forms for the 3PL and SGR models. Parallel Forms_25 items 3PL To use this workbook, download it to a desired folder and double click on the Parallel Forms_25 items 3PL.xls icon. The workbook contains two worksheets labeled "All items" and "FormA&B." Paste your item parameters (b, a, c) into the "All items" worksheet. Next, select the first five columns, A through E, as shown below (shaded cells). Assuming you pasted parameters for only 10 items the contents of the unshaded cells can be deleted.  Next, sort the a-parameters in descending order and color code items having similar a-values. Also update the number of items in the blue cell.  Next, select columns A through E and sort the b-parameters in ascending order (easy to difficult). Now you can easily assemble two forms by assigning items to each based on the b-values and the color codes.  Then, paste the item parameters for both forms into the appropriate cells of the worksheet named "FormsA&B." Compare the resulting TIFs and TCCs, and switch items as necessary until the desired level of overlap is achieved. Representative plots for two parallel forms are shown below.  To download a sample workbook to create parallel forms using the SGR model (5 options) click here. |