The implications of using a broad versus narrow set of criteria in research

Abstract

The Fukuda et al. criteria is the most widely used clinical case definition for diagnosing patients with chronic fatigue syndrome (CFS). Despite the frequency with which the Fukuda criteria are applied, the list of symptoms outlined in this case definition were not well enough specified to be easily applied to research settings. In 2005, Reeves et al. laid out a set of standards for operationalizing the Fukuda definition, specifying scales and cutoff scores for measuring the symptom criteria. This operationalization, often known as the empirical criteria, has been shown to identify an unexpectedly large number of patients, seemingly widening the net of inclusion for CFS diagnostic criteria. However, in a recent study in 2016 by Unger and colleagues it has been suggested that the 2005 Reeves et al. 2005 operationalization of the Fukuda criteria does not over-identify the number of patients with CFS as had been previously reported. This article reviews prior studies which provide context for these findings and offers a possible explanation for the discrepancies. Clearly, determining what case definition to use and how to operationalize it remains an important activity for scientists in this field, as it will influence work in multiple domains, including etiology, pathophysiology, epidemiology and treatment. We review these new findings, putting them in context and trying to highlight some of the reasons for the dramatic shifts in CFS prevalence rates across various studies.Most notably, the Center for Disease Control (CDC) estimates of CFS prevalence rates have increased dramatically over the years. In 2003, Reyes et al. published a prevalence study using the traditional approach to diagnosing CFS via Fukuda and found a prevalence rate of .24% in Wichita, Kansas [5].1 This rate was somewhat comparable to a previous population prevalence study in Chicago, which found a rate of .42% [6], again using the traditional approach to the Fukuda criteria. However, in a subsequent CDC population based study in Georgia, using the 2005 Reeves et al. empirical criteria, Reeves and colleagues concluded that the CFS prevalence rate had risen to 2.54% [4], which represents a 10-fold increase compared to the earlier CDC estimates. One explanation for the 10-fold increase is that cases of CFS did indeed increase over time, though this seems unlikely. When Jason and colleagues [7] conducted a follow-up to their original communitybased prevalence study [6] using the same traditional approach to diagnosing with the Fukuda criteria, they found that 10 years later CFS prevalence rates had remained relatively stable [7]. In light of this, other explanations for the increase in CDC prevalence rates need to be explored.