Lower Quadrant Edema Patient-Reported Outcome Measure Is Reliable, Valid, and Efficient for Patients With Lymphatic and Venous Disorders

Abstract

Objective: The main aims of this study were: (1) to create a patient-reported outcome measure (PROM) item bank for measuring the impact of lower quadrant edema (LQE) on physical function using item response theory and (2) to assess reliability, validity, and administration efficiency of LQE PROM scores based on computerized adaptive test (CAT) and the reliability of a 10-item short form (SF).

Methods: This retrospective study included data from patients treated in outpatient rehabilitation clinics for lower quadrant edema who responded to all 30 candidate items at intake. Item response theory model assumptions of unidimensionality, local item independence, item fit, and presence of differential item functioning (DIF) were evaluated. LQE-CAT-generated scores were assessed for reliability, validity, and administration efficiency. LQE-SF-generated scores were assessed for reliability.

Results: The total cohort included 4894 patients (mean [SD] age = 65 [14] years; range = 14-89 years). A set of 20 items was selected for the item bank based on support for its unidimensionality and fit to the item response theory model, with reliability estimates greater than 0.92 for CAT and SF administration modes. No items demonstrated DIF with respect to tested variables. After controlling for scores at intake, scores discriminated among multiple patient groups in clinically logical ways with better outcomes observed for patients who were younger with less chronic symptoms and fewer comorbidities. Scores were responsive to change but the effect size was small (0.4). There were negligible floor and ceiling effects. CAT administration of the item bank required an average of 6.1 items (median = 5). Scores correlated highly with full-bank scores (Pearson correlation coefficient = 0.98).

Conclusion: Scores on the LQE PROM were reliable, valid, and efficient for assessing perceived physical function of patients with lower quadrant edema. The LQE, CAT, and SF are suitable for research and routine clinical care. Reasons for the small effect size for change scores should be studied.

Impact: The newly developed LQE PROM was reliable and valid and offered efficient administration modes for assessing perceived physical function of patients with LQE, both for research and routine clinical care in busy outpatient rehabilitation settings. As an item response theory-based measure, the LQE PROM allows administration of condition-specific functional questions with low response burden for patients. The 10-item LQE-SF offers a feasible alternative administration mode when CAT administration is not available. This study supports a transition to PROMs that are based on modern measurement approaches to achieve the combined benefits of high accuracy and efficiency.

Keywords: Computerized Adaptive Testing; Item Response Theory; Lower Quadrant Edema; Lymphedema; Patient-Reported Outcome Measures; Physical Function.