Psychometric Evaluation of the PROMIS® Fatigue Measure in an Ethnically and Racially Diverse Population-Based Sample of Cancer Patients

Abstract

Aims:

Fatigue is the most prevalent and distressing symptom related to cancer and its treatment affecting functioning and quality of life.  In 2010, the National Cancer Institute’s Clinical Trials Planning Meeting on cancer-related fatigue adopted the PROMIS^® Fatigue measure as the standard to use in clinical trials.  This study evaluates the psychometric properties of the PROMIS fatigue measure in an ethnically/racially diverse population-based sample of adult cancer patients.

Methods:

Patients were recruited from four US cancer registries with oversampling of minorities.  Participants completed a paper survey 6 - 13 months post-diagnosis.  The 14 fatigue items (5-point Likert-type scale; English-, Spanish-, and Chinese-versions) were selected from the PROMIS fatigue short forms and larger item bank.  Item response theory and factor analyses were used to evaluate item- and scale-level performance.  Differential item functioning (DIF) was evaluated using the Wald test and ordinal logistic regression (OLR) methods.  OLR-identified items with DIF were evaluated further for their effect on the scale scores (threshold r² > .13).

Results:

The sample included 5,507 patients (2,278 non-Hispanic Whites, 1,122 non-Hispanic Blacks, 1,053 Hispanics, and 917 Asians/ Pacific Islanders); 338 Hispanics were given the Spanish-language version of the survey and 134 Asians the Chinese version.  One PROMIS item had poor discrimination as it was the only positively worded question in the fatigue measure.  Among Hispanics, no DIF was found with the Wald test, while the OLR method identified five items with DIF comparing the English and Spanish versions; however, the effect of DIF on scores was negligible (r² ranged from .006 - .015).  For the English and Chinese translations, no single item was consistently identified by both DIF tests.  Minimal or no impact was observed on the overall scale score comparisons among Whites, Blacks, Hispanics, and Asians using the English language scales.  However, greater numbers of items with DIF appeared when comparing Asians/ Pacific Islanders with Whites, Blacks, and Hispanics.  “How often were you too tired to think clearly†showed consistent DIF.

Conclusions:

Twelve of 14 PROMIS fatigue items performed well across the ethnically/racially diverse samples with minimal findings of DIF that would have any effect on comparing or combining scores across cancer populations.  Supporting evidence of the validity and reliability of the PROMIS measures will enhance the adoption of the measures in oncology clinical research.