A comparison of 4 questionnaires to measure fatigue in postpoliomyelitis syndrome.

Objective: To assess the comparability and reproducibility of 4 questionnaires used to measure fatigue in postpoliomyelitis syndrome (PPS).
Design: Repeated-measures at a 3-week interval.
Setting: University hospital.
Participants: Convenience sample of 65 patients with PPS.
Interventions: Not applicable.
Main Outcome Measures: The Fatigue Severity Scale (FSS), the Nottingham Health Profile (NHP) energy category, the Polio Problem List (PPL) fatigue item, and the Dutch Short Fatigue Questionnaire (SFQ).
Results: Correlations of scores between questionnaires were all significant (P<.01) and ranged from.43 (between the NHP energy category and the PPL fatigue item) to.68 (between the PPL fatigue item and the SFQ). Scores on the second visit, normalized to a 0 to 100 scale, were: FSS, 78+/-15; NHP energy category, 47+/-35; PPL fatigue item, 81+/-17; and SFQ, 65+/-22. Except for the difference between the FSS and the PPL fatigue item, the differences in scores between the questionnaires were significant (P<.01). Scale analysis indicated that all questionnaires measured the same unidimensional construct. The reproducibility of the FSS, the PPL fatigue item, and the SFQ was moderate. The smallest detectable change was 1.5 points for the FSS, 2.0 points for the PPL fatigue item, and 1.9 points for the SFQ.
Conclusions: Although the questionnaires measure the same fatigue construct in PPS, the results are not interchangeable because the ranges of measurement differ. The NHP energy category, in particular, appeared to have a high detection threshold. The moderate reproducibility of the questionnaires indicates a lack of precision, especially when applied at the individual patient level.