Source: Journal of Disability Policy Studies Online
Date: October 21, 2008
URL: http://jdps.sagepub.com http://dps.sagepub.com/cgi/content/abstract/1044207308325995v1
Evaluating the Centers for Disease Control's Empirical Chronic Fatigue
Syndrome Case Definition
Leonard A. Jason(*), Natasha Najar, Nicole Porter, Christy Reh,
DePaul University, Chicago, Illinois
* Address correspondence to Leonard A. Jason, PhD, Director, Center for
Community Research, DePaul University, 990 W. Fullerton Avenue, Suite 3100,
Chicago, IL 60614; e-mail: Ljason@depaul.edu
The Centers for Disease Control and Prevention (CDC) recently developed an
empirical case definition that specifies criteria and instruments to diagnose
chronic fatigue syndrome (CFS) in order to bring more methodological rigor to
the current CFS case definition. The present study investigated this new
definition with 27 participants with a diagnosis of CFS and 37 participants
with a diagnosis of a Major Depressive Disorder. Participants completed
questionnaires measuring disability, fatigue, and symptoms. Findings
indicated that 38% of those with a diagnosis of a Major Depressive Disorder
were misclassified as having CFS using the new CDC definition
. Given the
CDC's stature and respect in the scientific world, this new definition might
be widely used by investigators and clinicians. This might result in the
erroneous inclusion of people with primary psychiatric conditions in CFS
samples, with detrimental consequences for the interpretation of
epidemiologic, etiologic, and treatment efficacy findings for people with
Keywords: chronic fatigue syndrome; empirical case definition; Centers for
Disease Control and Prevention; Fukuda criteria; Major Depressive Disorders
Chronic fatigue syndrome (CFS) is a disabling chronic illness that has been
defined by a consensus-based approach by Fukuda et al. (1994). This case
definition specifies that individuals with this illness must have 6 or more
months of chronic fatigue of new or definite onset, which is not
substantially alleviated by rest, is not the result of ongoing exertion, and
results in substantial reductions in occupational, social, and personal
activities. In addition, to be diagnosed with this illness, individuals must
have four or more symptoms (i.e., sore throat, lymph node pain, muscle pain,
joint pain, postexertional malaise, headaches of a new or different type,
memory and concentration difficulties, and unrefreshing sleep) that persist 6
or more months since onset. Although the Fukuda et al. case definition
continues to be widely used, several articles have identified difficulties
that this case definition continues to pose to clinicians and researchers
(Jason, King, et al., 1999; Reeves et al., 2003). For example, the Fukuda et
al. case definition did not specify which instruments to use and did not
provide empirically derived cutoff points and scoring guidelines to diagnose
The Centers for Disease Control and Prevention (CDC) has now developed an
empirical case definition for CFS that involves assessment of symptoms,
disability, and fatigue (Reeves et al., 2005). The new CDC empirical case
definition assesses disability using the Medical Outcomes Survey
Short-Form-36 (Ware, Snow, & Kosinski, 2000), assesses symptoms using the
Symptom Inventory (Wagner et al., 2005), and assesses fatigue using the
Multidimensional Fatigue Inventory (Smets, Garssen, Bonke, & DeHaes, 1995).
The authors of this empirical case definition feel that the specification of
instruments and cutoff points would result in a more reliable and valid
approach for the assessment of CFS. Using these new criteria, the estimated
rate of CFS has increased to 2.54% (Reeves et al., 2007), a rate that is
about 10 times higher than prior CDC estimates (Reyes et al., 2003) and
prevalence estimates of other investigators (Jason, Richman, et al., 1999).
It is of interest that the new CFS rates are within the range of several mood
disorders. Mood disorders are the most prevalent psychiatric disorders after
anxiety disorders: For a major depressive episode, the 1-month prevalence is
2.2%, and lifetime prevalence is 5.8% (Regier, Boyd, & Burke, 1988). It is at
least possible that the increases in the United States are due to a
broadening of the case definition and possible inclusion of cases with
primary psychiatric conditions. CFS and depression are two distinct disorders, however, even if they share a number of common symptoms.
patients with a primary psychiatric illness in the current CFS case
definition could confound the interpretation of epidemiologic and treatment
studies. Major Depressive Disorder (MDD) is an example of a primary
psychiatric disorder that has some overlapping symptoms with CFS.Fatigue, sleep disturbances, and poor concentration occur in both depression and CFS. It is important to differentiate those with a principal diagnosis of MDD from those with CFS only.
This is particularly important because it is
possible that some patients with MDD also have chronic fatigue and four minor
symptoms that can occur with depression (e.g., unrefreshing sleep, joint
pain, muscle pain, and impairment in concentration). Fatigue and these four
minor symptoms are also defining criteria for CFS. It is possible that using
this broadened new CFS empirical case definition (Reeves et al., 2005), some
patients with a primary affective disorder could be misdiagnosed as having
CFS. Some CFS investigators would not see this as a problem because they
believe that CFS is mainly a psychiatric disorder and that distinctions
between the two phenomena are superficial and merely a matter of
nomenclature. However, several CFS symptoms, including prolonged fatigue after physical exertion, night sweats, sore throats, and swollen lymph nodes, are not commonly found in depression
. In addition, although fatigue is the
principal feature of CFS, fatigue does not assume equal prominence in
depression (Friedberg & Jason, 1998; Komaroff et al., 1996). Moreover,
illness onset with CFS is often sudden, occurring over a few hours or days,
whereas primary depression generally shows a more gradual onset. Individuals
with CFS can also be differentiated from those with depression by recordings
of skin temperature levels and electrodermal activity (Pazderka-Robinson,
Morrison, & Flor-Henry, 2004). Hawk, Jason, and Torres-Harding (2006) used
discriminant function analyses to identify variables that successfully
differentiated patients with CFS, MDD, and controls. Using percentage of time
fatigue was reported, postexertional malaise severity, unrefreshing sleep
severity, confusion/disorientation severity, shortness of breath severity,
and self-reproach to predict group membership, 100% were classified
correctly. In summary, CFS and depression are two distinct disorders,
although they share a number of common symptoms. It is possible to
appropriately differentiate MDD from CFS if one uses appropriate measures.
It is still unclear whether the new empirical case definition of CFS (Reeves
et al., 2005) has inappropriately included cases of purely affective
disorders, such as MDD. This study evaluated whether the CDC empirical case
definition distinguished between persons with MDD and persons with CFS. By
assessing samples with MDD and CFS, we hoped to clarify whether the CDC
empirical case definition has been able to successfully differentiate those
with MDD from those with CFS.
We recruited a total of 64 individuals, 27 with CFS and 37 with MDD. We
obtained our sample of participants with CFS from two sources: local CFS
support groups in Chicago and a previous research study conducted at DePaul
University. To be included in the study, participants were required to have
been diagnosed with CFS, using the Fukuda et al. (1994) diagnostic criteria,
by a certified physician and were required to currently meet CFS criteria
using the Fukuda et al. criteria. We excluded individuals who had other
current psychiatric conditions in addition to major depression or who
reported having untreated medical illnesses (e.g., diabetes, anemia).
We solicited 37 participants with a diagnosis of MDD to participate in this
study. We found participants from three sources: local chapters of the
Depression and Bipolar Support Alliance group in Chicago; Craigslist, a free
local classified ads forum that is community moderated; and online depression
support groups. To be included in the study, all participants were required
to have been diagnosed with MDD by a licensed psychologist or psychiatrist.
We excluded individuals who had other current psychiatric conditions in
addition to MDD (e.g., bipolar, schizophrenia) and those who reported having
untreated medical illnesses.
Participants who met criteria completed questionnaires that are described
below. Participants reported any previous physical and mental illnesses and
the date of diagnosis as well as current medications being taken to ensure
that no other illness could account for the fatigue. We carefully screened
participants to ensure that participants from the MDD group did not have CFS
as defined by the Fukuda et al. (1994) criteria.
We collected basic demographic variables that included age, ethnicity,
marital status, occupation, gender, work status, and educational level.
The Medical Outcomes Survey Short-Form-36.
This 36-item instrument is composed of multi-item scales that assess
functional impairment in eight areas: limits in physical activities (Physical
Function), limits in one's usual role activities due to physical health (Role
Physical), limits in one's usual role activities due to emotional health
(Role Emotional), Bodily Pain, general health perceptions (General Health),
vitality (Energy and Fatigue), Social Function, and General Mental Health
(Ware et al., 2000). Scores in each area reflect ability to function, and
higher values indicate better functioning. Reliability and validity studies
have demonstrated high reliability and validity in a wide variety of patient
populations for this instrument (Stewart, Greenfield, Hays, et al., 1989).
Based on the CDC empirical case definition (Reeves et al., 2005), the Medical
Outcomes Survey Short-Form-36 was used to assess disability (Wagner et al.,
2005). According to Reeves et al. (2005), significant reductions in occupa-
tional, educational, social, or recreational activities were defined as
scores lower than the 25th percentile on Physical Function (less than or
equal to 70), or Role Physical function (less than or equal to 50), or Social
Function (less than or equal to 75), or Role Emotional function (less than or
equal to 66.7). A person would meet the disability criterion for the
empirical CFS case definition by showing impairment in only one or more of
these four areas (Reeves et al., 2005).
The CDC Symptom Inventory.
The CDC Symptom Inventory assesses information about the presence, frequency,
and intensity of 19 fatigue-related symptoms during the past 1 month (Wagner
et al., 2005). All 8 of the critical Fukuda et al. (1994) symptoms were
included as well as 11 other symptoms (e.g., diarrhea, fever, sleeping
problems, and nausea). For each of the 8 Fukuda et al. symptoms,
participants were asked to report the frequency (1 = a little of the time, 2
= some of the time, 3 = most of the time, 4 = all of the time) and severity
(the ratings were transformed to the following scale: .08 = very mild, 1.6 =
mild, 2.4 = moderate, 3.2 = severe, 4 = very severe; see Note 1). The
frequency and severity scores were multiplied for each of the 8 critical
Fukuda et al. symptoms and were then summed. Participants having 4 or more
symptoms and scoring greater than or equal to 25 would meet symptom criteria
on this instrument according to the CDC empirical case definition (Reeves et
The Multidimensional Fatigue Inventory.
This instrument is a 20-item self-report instrument consisting of five
scales: General Fatigue, Physical Fatigue, Reduced Activity, Reduced
Motivation, and Mental Fatigue (Smets et al., 1995). Each scale contains four
items rated from 1 to 5, with the scale score of 1 meaning yes, that is true
and the scale score of 5 meaning no, that is not true. Reeves et al. (2005)
used the Multidimensional Fatigue Inventory to measure severe fatigue, and to
do this, they used only two of the five subscales: General Fatigue and
Reduced Activity. Using the CDC empirical case definition standards, severe
fatigue was defined as greater than or equal to 13 on General Fatigue or less
than or equal to 10 on Reduced Activity.
Classification by CDC Empirical Case Definition CriteriaWhen using the CDC empirical case definition to classify people with CFS, all
27 participants in the CFS-recruited group met criteria for CFS. However, 14
additional individuals from the MDD group also met the new CDC criteria for
CFS. That is, 38% of those with a professional diagnosis of major depression
were misclassified as having CFS using the CDC empirical case definition.
Participants were separated into three groups: Those 27 diagnosed with CFS
prior to this study and who met the new empirical CDC case definition of CFS,
those 14 from the group with MDD meeting the new empirical CDC case
definition of CFS criteria (MDD/CFS), and those 23 from the group with MDD
not meeting the new empirical CDC criteria for CFS (MDD). Sociodemographic
data were compared across all three groups of participants using Pearson's
chi^2 and analysis of variance (ANOVA; see Table 1). Findings indicated a
significant age effect, F(2,63)=3.25, p<.05. The average age for the CFS
group was significantly older than the MDD/CFS group. Furthermore, there were
also significant differences in regard to work status between groups,
chi^2(6,N=64)=13.92, p<.05. More individuals in the CFS group were on
disability as compared to the MDD/CFS group, chi^2(1,N=41)=4.11, p<.05.
Illness Classification by Standardized Clinically Empirical Criteria
Medical Outcomes Survey Short-Form-36.
According to the CDC empirical case definition, participants are required to
demonstrate functional impairment within one of the four areas: Physical
Function, Role Physical, Role Emotional, and Social Function. One-way ANOVA
was used to assess the effect of physical impairment within four subscales of
the Medical Outcomes Survey Short-Form-36 for the three groups (CFS, MDD, and
MDD/CFS). As seen in Table 2, there were significant effects for three of the
subscales, but not social functioning. Using Tukey's honestly significant
difference (HSD) post hoc test, significant differences were found for Role
Physical; participants with CFS had significantly lower scores compared to
both the MDD group (p<.001) and the MDD/CFS group (p<.001). In regard to
physical functioning, the participants with CFS had significantly worse
Physical Function impairment scores in compari- son to participants with MDD
(p>.001) and participants with MDD/CFS (p<.001). Finally, for role emotional
functioning, the MDD/CFS group scored significantly lower on the Role
Emotional scale than both the CFS (p<.001) and the MDD groups (p<.001).
Examining Table 3, it is apparent that all three illness groups met criteria
for at least one of the four subscales and thus would meet the disability
criteria for the empirical case definition of CFS. It is clear that
significantly more participants from the MDD and MDD/CFS groups met Role
Emotional criteria than the CFS group. However, if Role Physical or Physical
Functioning criteria were used as the sole criterion for disability, sig-
nificantly more participants within the CFS group would meet the disability
criteria than those in the MDD/CFS and MDD groups.
Symptom Inventory analysis.
There was a significant effect of the total CFS symptom scores,
F(2,61)=34.184, p<.001. The MDD group had the lowest mean score, indicating
that this group did not likely meet criteria for CFS. The CFS group mean
score was directionally but not significantly higher than the MDD/CFS group
score. Tukey post hoc tests indicated that the CFS and MDD/CFS groups scored
significantly higher than the MDD group (p<.001). Examining Table 3, both the
CFS and MDD/CFS groups had higher percentages of participants meeting CFS
symptom criteria than those in the MDD group. The fact that 100% of
participants in the CFS and MDD/CFS groups met criteria for this index
suggests that many individuals without CFS will meet these cutoff criteria
for symptom frequency and severity.
The Multidimensional Fatigue Inventory.
The CDC empirical case definition used the Multidimensional Fatigue Inventory
to measure fatigue. There was a significant effect for General Fatigue,
F(2,61)=4.89, p<.05, but no significant effect was found for Reduced
Activity. Post hoc analysis using the Tukey HSD test revealed significant
differences for General Fatigue. The MDD group scored significantly lower on
the General Fatigue scale than both the CFS (p<.01) and MDD/CFS groups
(p<.01). Inspecting Table 3, all participants within the CFS and MDD/CFS
groups met one of the fatigue criteria. In addition, 87% of those in the MDD
group also met one of the fatigue criteria. This again suggests that for the
domain of fatigue, the empirical case criteria will select many individuals
without CFS who will meet fatigue criteria for the empirical case definition.
Reeves et al. (2005) claim that the empirical definition identifies people
with CFS in a more precise manner than can occur in the more traditional way
of diagnosis. Analyses from this study reveal that the new empirical case
definition identified 38% of the MDD group as meeting CFS criteria. Cantwell
(1996) argues that diagnostic criteria should specify which diagnostic
instrument to use, what type of informants to interview, and how to determine
the presence and severity of the criteria. The effort by Reeves et al. to
specify a certain number and type of symptoms that should be present in order
to make a particular diagnosis appears to be overinclusive, particularly for
those having a primarily depressive disorder.
An analysis of the Medical Outcomes Survey Short-Form-36 illustrates the
problems with the cutoff criteria. When using the Reeves et al. (2005) cutoff
points to classify functional impairment, all three groups (100%) met
criteria for this instrument in Table 3. However, had Reeves et al. selected
either Physical Function or Role Physical, better differentiation would have
occurred, as there is a significant difference between the CFS group and the
other two groups for these domains. Because individuals need only to score
lower than the 25th percentile in one of these four areas in order to meet
the CFS criteria, individuals might not have any reductions in key areas of
physical functioning and only impairment in role emotional areas (e.g.,
problems with work or other daily activities as a result of emotional
For Role Emotional, 93% of the MDD/CFS group and 78% of the MDD group met
criteria, a percentage much higher than the CFS group (44%). Ware et al.
(2000) found that the mean for Role Emotional for a clinical depression
group was 38.9, indicating that almost all those with clinical depression
would meet criteria for being within the lower 25th percentile on this scale
(which was a score of less than or equal to 66.7). In addition, King and
Jason (2005) compared a group diagnosed with CFS and a group diagnosed with
MDD, and the latter group had lower scores than the group with CFS (37.8 vs.
48.9), but both groups would have met the CDC criteria as they both scored
below 66.7. In contrast, if the criterion was a score lower than the 25th
percentile on just Physical Function (less than or equal to 70), the
participants with CFS would have met this criterion as their average score
was 44, whereas many within the MDD group would have not met this criterion
as their average score was 70.3.
Regarding the Symptom Inventory, 100% of both the CFS and MDD/CFS groups met
criteria, indicating this instrument did not distinguish the individuals with
CFS from individuals with major depression. It is probable that the Symptom
Inventory misclassified the MDD/CFS group for several reasons. For example,
the Symptom Inventory asks about the symptom occurrences within the past
month rather than the past 6 months, as required by the Fukuda et al. (1994)
case definition. The requirement for a participant to report a symptom for 1
month might include more individuals within the CFS category (e.g., a person
who has experienced a physical illness such as influenza or a head cold could
very well have experienced a severe sore throat for the past month). Even
with summed scores for the empirical case definition needing to be greater
than or equal to 25 (Reeves et al., 2005), the overall level of symptoms
might be relatively low for patients with classic CFS symptoms (the criterion
would be met if an individual rated only two symptoms as occurring all the
time, and one was of moderate and the other of severe severity). Similarly, a
person with MDD could endorse symptoms that would easily meet criteria for
this scale, such as unrefreshing sleep, impaired memory, and headaches, and
muscle pain at a moderate to severe level. However, the most important factor
is that the Symptom Inventory does not distinguish critical symptoms for CFS
such as postexertional malaise, unrefreshing sleep, and cognitive
difficulties. Each symptom is given the same value, which means that a
participant reporting severe and frequent headaches is given the same value
as a participant reporting severe and frequent postexertional malaise.
Overall, 14 individuals diagnosed with MDD scored 25 or higher on the Symptom
Inventory and reported four or more symptoms. This demonstrates thatindividuals with primary psychiatric illnesses are not always excluded using the CDC Symptom Inventory.
The Multidimensional Fatigue Inventory was used to measure severe fatigue,
yet 93% of both the CFS and MDD/CFS groups met criteria for General Fatigue,
while 74% of the MDD group did as well. As for the criteria that Reeves et
al. (2005) used, the primary developer of the Multidimensional Fatigue
Inventory had this to say: "Regarding the criteria suggested by Reeves, we
have no paper to back up their decision, but scanning their paper it appears
that they used the median of their own data" (E. M. Smets, personal
communication, June 29, 2006). In one study of three groups with CFS, the
mean Multidimensional Fatigue Inventory General Fatigue scores were 18.3 to
18.8 (Tiersky, Matheis, DeLuca, Lange, & Nateson, 2003). When assessing
Reduced Activity, 85% and 86% of both the CFS and MDD/CFS groups
(respectively) met criteria, as did 78% of the MDD group. Therefore, 100% of
the CFS and 100% of the MDD/CFS group met the CDC fatigue criteria. The
problem with this instrument is that it is relatively easy to meet criteria
for one of the two categories. In other words, a depressed person could
easily respond positively to questions such as "I get little done" or "I do
very little in a day" and answer negatively to "I feel very active" or "I
think I do a lot in a day." Consequently, a depressed person would meet CFS
criteria by answering "entirely true" to these types of items.
Inspecting the scores of a person with MDD who was inappropriately classified
as having CFS highlights the problems with the CDC empirical criteria. A
26-year-old female with MDD met criteria for CFS using the CDC empirical case
criteria (Reeves et al., 2005). For the Medical Outcomes Survey
Short-Form-36, she met cutoff points for Social Function (scoring 37.5 when
needing to score 75) and Role Emotional (scoring 0 when needing to score
66.7). With a clinical diagnosis of MDD, she demonstrated impairment with
social and emotional functioning, two important traits of depression. This
person scored 100 on Physical Function, which is the highest possible score
on this measure, indicating that she had no difficulties with physical
functioning, which would be a clear indicator that she did not have CFS. On
the CDC Symptom Inventory, she reported that postexertional malaise was mild
only some of the time, indicating that she did not have this cardinal symptom
of CFS. For this individual and others within the MDD/CFS group, the
instruments used to identify cases of CFS did not adequately exclude persons
with primary psychiatric disorders.
There were biases in using a convenience sample, and recruitment from a
population-based referral source would have been preferable, but such samples
are expensive to recruit. Also, the sample sizes overall were relatively
small, but even though power was low to detect differences, we were able to
find a number of significant outcomes, as represented in Tables 2 and 3. In
addition, we focused on only one psychiatric disorder, and future studies
might include anxiety disorders, which might also be misclassified. In
addition, there is probably a redundancy in some of our findings, as some of
the scales are correlated.
There are other ways that might be used to develop improvements in the CFS
case definition. As an example, Jason, Corradi, and Torres-Harding (2007)
factor analyzed the core symptoms as defined by the Fukuda et al. (1994)
criteria, but this did not result in interpretable factors. However, when
they included a larger group of theoretically defined symptoms in the factor
analyses, an interpretable set of factors did emerge. The following factors
were found: neurocognitive (e.g., slowness of thought), vascular (e.g., dizzy
after standing), inflammation (e.g., chemical sensitivities), muscle/joint
(e.g., pain in multiple joints), infectious (e.g., sore throat), and
sleep/postexertional (e.g., unrefreshing sleep).
These findings suggest that
theoretical and empirical approaches to determining critical symptoms of CFS
have considerable merit. The field of CFS studies needs to be grounded in
empirical methods for determining a case definition versus more
consensus-based efforts.In conclusion, this study suggests that the Reeves et al. (2005) empirical case definition has broadened the criteria such that some individuals with a purely psychiatric illness will be inappropriately diagnosed as having CFS.
The Reeves et al. empirical case definition used specific instruments (such
as the Medical Outcomes Survey Short-Form-36) to make diagnostic decisions
but included dimensions within them such as role emotional functioning that
were not specific for this illness. Green, Romei, and Natelson (1999) found
that 95% of individuals seeking medical treatment for CFS reported feelings
of estrangement, and 70% believed that others uniformly attributed their CFS
symptoms to psychological causes. Inappropriate inclusion of pure
psychiatric disorders into the CFS samples may further contribute to the
diagnostic skepticism and stigma that individuals with this illness
encounter. Several researchers continue to believe that CFS should be
considered a functional somatic syndrome (Barsky & Borus, 1999),
characterized by diffuse, poorly defined symptoms that cause significant
subjective distress and disability and that cannot be corroborated by
consistent documentation of organic pathology. Taylor, Jason, and Schoeny
(2001) have challenged this position, but ultimately assessment and criteria
that fail to capture the unique characteristics of these illnesses might
inaccurately conclude that only distress and unwellness characterize CFS,
thus inappropriately supporting a unitary hypothetical construct called
"functional somatic syndrome." Such blurring of diagnostic categories will
make it even more difficult to identify biological markers for this illness,
and if they are not identified, many scientists will be persuaded that this
illness is psychogenic (Jason & Richman, 2008). Ultimately, using a broad or
narrow definition of CFS will have important influences on CFS epidemiologic
findings, on rates of psychiatric comorbidity, on how patients are treated,
and ultimately on the likelihood of finding biological markers for this
1. The scale we used had five choices, and we needed to convert the ratings
to a 4-point scale. We divided the five items by 4, which came to .8. We
then made each increment in value .8.
About the Authors
Leonard A. Jason, PhD, is a professor of psychology at DePaul University and
the Director of the Center for Community Research. His current interests
include myalgic encephalomyelitis/chronic fatigue syndrome, recovery homes,
and tobacco control.
Natasha Najar, BA, currently conducts research at Northwestern University.
She has particular interests in cultural issues.
Nicole Porter, PhD, currently is the project director of a chronic fatigue
syndrome (CFS) epidemiologic grant at the Center for Community Research,
DePaul University. Her interests are in myal- gic encephalomyelitis/CFS,
meditation, and dynamic systems.
Christy Reh, BA, currently is a graduate student at the Alder School of
Professional Psychology in Chicago, Illinois.
Table 1. Sociodemographic Characteristics Between the CFS, MDD/CFS, and MDD Groups
Characteristic CFS MDD/CFS MDD Significance
-------------------- -------------------- --------------------
n % M (SD) n % M (SD) n % M (SD)
Age 27 49 (13.2) 14 37 (12.3) 23 44 (15.5)
Male 2 7 1 7 3 13
Female 25 93 13 93 20 87
White 19 70 11 79 17 74
Black 5 19 2 14 0 0
Other 3 11 1 7 6 26
Married 7 26 3 21 4 17
Never married 11 41 8 57 15 65
Separated/widowed/divorced 9 33 3 21 4 17
Yes 17 63 5 36 8 35
No 10 37 9 64 15 65
High school degree or less 2 7 2 14 4 17
Partial training 9 33 8 57 6 26
College degree 8 30 3 21 7 30
Grad/profession 8 30 1 7 6 26
On disability 13 48 3 21 3 13 *
Unemployed 4 15 2 14 7 31
Work part-time 5 18 2 14 1 4
Work full-time 5 18 7 50 12 52
Note: CFS=chronic fatigue syndrome; MDD=major depressive disorder.
*Difference is statistically significant at the p=<.05 level.
Table 2. Mean Differences Between the CFS, MDD/CFS, and MDD Groups on Criteria Variables
Variable CFS MDD/CFS MDD Significance
------------------- ------------------- -------------------
M (SD) M (SD) M (SD)
Medical Outcomes Survey Short-Form-36
Role Physical 5.56 (16.01)^a,b 51.79 (40.98)^b 58.7 (45.61)a ***
Social Function 30.09 (28.43) 41.96 (23.31) 40.22 (25.27)
Physical Function 37.41 (23.43)^a,b 70.36 (32.90)^b 76.74 (21.25)a ***
Role Emotional 69.14 (40.22)^a,b 19.05 (31.25)^a 30.43 (40.09)b ***
CDC Symptom Inventory
CDC scores 43.97 (14.28)^b 37.56 (10.54)^a 17.05 (8.62)a,b ***
Multidimensional Fatigue Inventory
General Fatigue 16.74 (2.90)^b 16.86 (2.80)^a 14.3 (3.42)a,b **
Reduced Activity 14.44 (3.79) 13.64 (3.95) 13.17 (4.77)
Note: Similar letter subscripts across rows indicate significant differences in means.
CFS=chronic fatigue syndrome; MDD=major depressive disorder.
**Difference is statistically significant at the p=<.01 level.
***Difference is statistically significant at the p=<.001 level.
Table 3. Percentages of the CFS, MDD/CFS, and MDD Groups Meeting
Specific CFS Criteria
Criteria %CFS %MDD/CFS %MDD Significance
Medical Outcomes Survey Short-Form-36
Role Physical 50.0 96^a,b 50^a 44^b ***
Social Function 75.0 96 100 91
Physical Function 70.0 93^a,b 43^a 35^b ***
Role Emotional 66.7 44^a,b 93^a 78^b ***
Meets at least 1 100 100 100
CDC Symptom Inventory
CDC scores 25.0 100^a 100^b 9^a,b ***
Multidimensional Fatigue Inventory
General Fatigue 13.0 93 93 74
Reduced Activity 10.0 85 86 78
Meets at least 1 100 100 87
Note: Similar letter subscripts across rows indicate significant differ-
ences in means. CFS=chronic fatigue syndrome; MDD=major depressive
***Difference is statistically significant at the p=<.001 level.
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(c) 2008 Hammill Institute on Disabilities
(c) 2008 SAGE Journals
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And if you're reading research on "CFS", be sure to read the selection criteria carefully. Tom Kindlon is pretty good at pulling out those studies which say they're investigating CFS but are actually looking at people with psychiatric problems.