Factor analysis of unexplained severe fatigue & interrelated symptoms: overlap with criteria for Chronic Fatigue Syndrome (CFS)

The objective of this study was to identify factors explaining the

correlations among unexplained severe fatigue of different

durations (1- 5 months or > or =6 months) and symptoms

reported as being significant health problems during a

preceding 4-week period. Between June and December of 1994, a

cross-sectional, random digit dialing telephone survey was

conducted among residents of San Francisco, California. All

subjects who reported having severe fatigue lasting for > or

=1 month and a random sample of nonfatigued subjects were

asked to participate in a detailed telephone interview. Data

from 1,510 individuals aged 18- 60 years who did not have

medical or psychiatric conditions that could explain their

severe fatigue were analyzed.

Common factor analyses

identified three correlated factors (defined as “fatigue-mood-

cognition” symptoms, “flu-type” symptoms, and “visual

impairment”) that explained the correlations among fatigue

lasting for > or =6 months and 14 interrelated symptoms. No

factor explained the correlations among fatigue lasting for

1-5 months and other symptoms.

The combination of fatigue of >

or =6 months’ duration and selected symptoms overlaps with

published criteria used to define cases of chronic fatigue

syndrome (CFS). Although symptoms described in this study were

reported as appearing within the preceding month, and CFS

symptoms must have been present for the previous 6 months,

these results provide empirical support for the interrelations

among unexplained fatigue of > or =6 months’ duration and

symptoms included in the CFS case definition.

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