Rapid detection of differential item functioning in assessments of health-related quality of life: The Functional Assessment of Cancer Therapy.
BACKGROUND
Differential item functioning (DIF) occurs when a test item functions differently in different groups when controlling for the level of the underlying construct measured by the test. DIF assessment is a first step in the evaluation of test bias. We sought to demonstrate a rapid hybrid approach to DIF detection by determining the presence and scale-level impact of DIF related to eight covariates in four domains measured by the Functional Assessment of Cancer Therapy (FACT).


RESULTS
The number of items found with DIF in each domain depended on the criterion chosen to define the presence of DIF. With a few exceptions, scale-level differential functioning was similar regardless of the criteria chosen. For physical well-being, there was relevant scale-level differential functioning related only to race. For social and family well-being, there was relevant scale-level differential functioning related to each of the covariates. For emotional well-being, there was relevant scale-level differential functioning related to ethnicity, language, and race. For functional well-being, there was relevant scale-level differential functioning related to ethnicity, race, education, and self- vs. interviewer-administration.


CONCLUSIONS
Our rapid hybrid approach to DIF detection may be broadly applicable in other studies of health-related quality of life.
Crane
Paul K
PK
Department of Medicine, University of Washington, Seattle, USA. pcrane@u.washington.edu
Gibbons
Laura E
LE
Narasimhalu
Kaavya
K
Lai
Jin-Shei
JS
Cella
David
D
D000293:Adolescent; D000328:Adult; D000368:Aged; D006305:Health Status Indicators; D006801:Humans; D008875:Middle Aged; D009369:Neoplasms / Q000628:therapy*; D011788:Quality of Life