Classical test theory and item response theory/Rasch model to assess differences between patient-reported fatigue using 7-day and 4-week recall periods

Objective: This study compared self-reported fatigue between 7-day and 4-week time frames and explored factors that affect patients' responses. Study Design and Setting: Two hundred and sixteen cancer patients completed either 7-day or 4-week version of the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F). Cochran-Mantel-Haenszel statistics and Cochran-Armitage trend tests were used to assess the association between time frame and item scores. Information function curves at both item and scale levels were depicted to evaluate the precision along the fatigue continuum. Differential item functioning (DIF) was used to examine the stability of the psychometric properties between time frames. Results: Time frame did not influence patients' item responses. Examination of information function curves at item level did not clearly favor either time frame. At the scale level, the 7-day time frame was slightly more precise overall than the 4-week time frame. No item demonstrated DIF between time frames. Neither gender nor fatigue severity had an impact on above results. Conclusion: This study suggests 7-day and 4-week time frame are equally appropriate in measuring fatigue, preference might be given to the more informative 7-day time frame. However, substantive considerations regarding the appropriate time frame should outweigh statistical ones. (C) 2009 Elsevier Inc. All rights reserved.