1. Item-Level Assessment of the Irritable Bowel Syndrome Quality of Life Questionnaire in Patients With Diarrheal Irritable Bowel Syndrome 
David A. Andrae, PhD, Paul S. Covington, MD, Donald L. Patrick, PhD, MSPH 
Clinical Therapeutics 
Volume 36, Issue 5, Pages (May 2014)
DOI: /j.clinthera
Copyright © 2014 The Authors Terms and Conditions

2. Figure 1
Comparison of estimated latent trait values (θ) for the constrained graded response model (CGRM), the unconstrained GRM (UGRM), and the testlet response model (TRM).
Clinical Therapeutics  , DOI: ( /j.clinthera )
Copyright © 2014 The Authors Terms and Conditions

3. Figure 2
Comparison of information functions, I(θ), for the constrained graded response model (CGRM), the unconstrained GRM (UGRM), and the testlet response model (TRM), with total information as determined by the area under each information curve.
Clinical Therapeutics  , DOI: ( /j.clinthera )
Copyright © 2014 The Authors Terms and Conditions

4. Figure 3
Effect of items with possible differential item functioning (DIF) due to sex on constrained graded response model estimates of the latent trait (θ).
Clinical Therapeutics  , DOI: ( /j.clinthera )
Copyright © 2014 The Authors Terms and Conditions

5. Figure 4
Effect of items with possible differential item functioning (DIF) due to sex on unconstrained graded response model estimates of the latent trait (θ).
Clinical Therapeutics  , DOI: ( /j.clinthera )
Copyright © 2014 The Authors Terms and Conditions

6. Figure 5
Effect of items with possible differential item functioning (DIF) due to sex on the testlet response model estimates of the latent trait (θ).
Clinical Therapeutics  , DOI: ( /j.clinthera )
Copyright © 2014 The Authors Terms and Conditions

7. Figure 6
Scatterplot matrix of the IBS-SSS, 34-item Irritable Bowel Syndrome Quality of Life (IBS-QOL) total score with the latent trait (θ) estimates from the constrained graded response model (CGRM), the unconstrained GRM (UGRM), and the testlet response model (TRM) vs the IBS-QOL total score for 32 items. The lower triangle represents scatterplots with regression lines overlaid, the diagonal depicts the data densities of the scores, and the upper triangle displays the Spearman correlation coefficients among the scores.
Clinical Therapeutics  , DOI: ( /j.clinthera )
Copyright © 2014 The Authors Terms and Conditions