Sirs, I read with interest the validation of the functional assessment of chronic illness therapy-fatigue (FACIT-F) in inflammatory bowel disease (IBD) by Tinsley et al.1 In recent years, there have been an increasing number of papers addressing the problem of fatigue in IBD, which of course is a positive development.
However, to be used as measurement tools in clinical trials, questionnaires used to measure fatigue must satisfy basic standards (including validity, reliability, sensitivity, responsiveness and reproducibility).2
The Fatigue Questionnaire (FQ) was originally developed by Chalder et al.3 and consists of 11 items that are divided into two main dimensions: physical fatigue (PF) and mental fatigue (MF). In addition to measuring episodic fatigue (irrespective of the duration of symptoms), the FQ contains two questions regarding the duration and extent of fatigue symptoms, which makes it possible to assess the prevalence of chronic fatigue, with a duration of more than 6 months.4
Recently, we validated the FQ in an IBD population;4, 5 however, as correctly noted by Tinsley et al.,1 we did not report the test-retest reliability of the FQ. This may of course cause grounds for speculations about whether the FQ is suitable for longitudinal assessments of fatigue in IBD or not.
In Table 1, I therefore present the test-retest results of the FQ in a subgroup of patients (n = 22) that were deemed to be in a stable condition after 6 months. The intra-class correlation coefficient reported in Table 1 is the single measure calculated using the two-way mixed model. The results confirm a high level of agreement between the two occasions, and I can therefore conclude that the FQ is suitable for prospective and longitudinal assessments of fatigue in IBD.
|Baseline mean (SD)||6 Months mean (SD)||ICC|
|MF||4.6 (1.4)||4.9 (1.5)||0.88|
|PF||9.5 (2.9)||9.5 (2.9)||0.98|
|TF||14.1 (3.6)||14.5 (3.4)||0.98|