Testlets are groups of locally dependent items, such as the questions about the same topic. How are you conceptualizing the testlets?

 

A. If the testlests are conceptualized as groups of separate items, then please put a testlet-code in column 1 of the item label. You can then obtain item-level summary statistics in Winsteps using ISUBTOTAL=1 and Table 27. You can also obtain person-by-testlet measures using DPF=1 and Table 31, and person-group-by-testlet using DPF=1, DIF=person group code column and Table 33.

 

B. If two or more items are highly dependent (so that their residuals are highly correlated in Table 23.99) , then it may be better combine them into one "testlet" item. Testlet Response Theory is  technically complex and requires special software, but we can approximate it by combining the dependent items into partial-credit items

 

From a Winsteps analysis of the separate items, Output files menu, RFILE= to Excel (with headings).

In Excel, sum the separate items into new combined-item columns. Save the Excel file

In Winsteps, Excel/RSSST menu, Excel option. Click on the saved Excel file. Select the combined items from the list of Excel columns. Format a Winsteps control and data file.  (You can also select the original uncombined items, but will need to weight them zero with IWEIGHT= in the new analysis.)

Analyze the new Winsteps control and data file with ISGROUPS=0  (partial-credit model)

 

Cross-plot the person measures from the original analysis and the partial credit analysis. Are there any differences? Which analysis produces more meaningful results?