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Psychometric properties of the CDC symptom inventory for the assessment of chronic fatigue syndrome.

Wagner D, Nisenbaum R, Heim C, Jones JF, Unger ER, Reeves WC
Psychometric properties of the CDC symptom inventory for the assessment of chronic fatigue syndrome Population Health Metrics 2005:3:8. (The complete electronic version of this article is available at http://www.pophealthmetrics.com/content/3/1/8 or through the Digital Object Identifier System [DOI] via doi:10.1186/1478-7954-3-8.)

Summary

Chronic fatigue syndrome is characterized by severe chronic (for six or more months) fatigue accompanied by four or more of the following symptoms: substantial impairment in short-term memory or concentration, sore throat, tender lymph nodes, muscle pain, multi-joint pain without swelling or redness, headaches of a new type, pattern, or severity, unrefreshing sleep, and post-exertional malaise lasting more than 24 hours. Because no characteristic physical signs or laboratory abnormalities have been identified for the illness, its diagnosis is made on the basis of patient-reported symptoms. An International CFS Study Group convened by CDC has recommended that CFS research studies categorize functional impairment by criteria on the Medical Outcomes Survey Short Form-36 and that they describe characteristics of the fatigue according to the Multidimensional Fatigue Inventory, and the Study Group recommended use of an instrument like the CDC Symptom Inventory to characterize presence, frequency, and severity of accompanying symptoms. The Study Group also recommended that CDC validate the Symptom Inventory by evaluating its psychometric properties. This study found that the Symptom Inventory has good internal consistency and excellent convergent validity. It is a reliable and valid instrument for use in assessing symptoms that accompany CFS, and it is particularly valuable because it allows other dimensions of the illness to be assessed.

Abstract

Objectives: Validated or standardized self-report questionnaires used in research studies and clinical evaluation of chronic fatigue syndrome (CFS) generally focus on the assessment of fatigue. There are relatively few published questionnaires that evaluate case defining and other accompanying symptoms in CFS. This paper introduces the self-report CDC CFS Symptom Inventory and analyzes its psychometric properties.

Methods: One hundred sixty-four subjects (with CFS, other fatiguing illnesses and non fatigued controls) identified from the general population of Wichita, Kansas were enrolled. Evaluation included a physical examination, a standardized psychiatric interview, three previously validated self-report questionnaires measuring fatigue and illness impact (Medical Outcomes Survey Short-Form-36 [SF-36], Multidimensional Fatigue Inventory [MFI], Chalder Fatigue Scale), and the CDC CFS Symptom Inventory. Based on theoretical assumptions and statistical analyses, we developed several different Symptom Inventory scores and evaluated them on their ability to differentiate between participants with CFS and non-fatigued controls.

Results: The Symptom Inventory had good internal consistency and excellent convergent validity. A Total score (all symptoms), Case Definition score (CFS case defining symptoms) and Short Form score (6 symptoms with minimal correlation) differentiated CFS cases from controls. Furthermore, both the Case Definition and Short Form scores distinguished people with CFS from fatigued subjects who did not meet criteria for CFS.

Conclusions: The Symptom Inventory appears to be a reliable and valid instrument to assess symptoms that accompany CFS. It is a positive addition to existing instruments measuring fatigue because it allows other dimensions of the illness to be assessed. Further research is needed to confirm and replicate the current findings in a normative population.

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