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.


METHODS
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.


CONCLUSIONS
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.
Lai
Jin-Shei
JS
Center on Outcomes, Research and Education, Evanston Northwestern Healthcare, Evanston, IL 60201, USA. js-lai@northwestern.edu
Cook
Karon
K
Stone
Arthur
A
Beaumont
Jennifer
J
Cella
David
D
D000328:Adult; D000368:Aged; D001294:Attitude to Health; D005221:Fatigue / Q000175:diagnosis* / Q000209:etiology; D005260:Female; D006801:Humans; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D015233:Models, Statistical; D009369:Neoplasms / Q000150:complications; D011594:Psychometrics; D012720:Severity of Illness Index; D013997:Time Factors