Does the use of the "Role emotional" subscale of the SF-36 help with sensitivity and specificity rates? Can we find out the prevalence rate if this subscale hadn't been used?
Tom Kindlon, Irish ME/CFS Support Group
15 June 2007
It is to be welcomed that attempts are being made to operationalize the CDC (94) CFS criteria [1], enabling easier comparisons between studies and making it easier for researchers to try to replicate findings.
So for example, having some sort of numerical value on a symptom so that one can say whether a symptom is present or not in a patient seems to be a good idea.
However if one is aiming to do this, it would seem preferable to choose methods that have good sensitivity and specificity rates for the condition in question. And it's questionnable whether the methods used in this study have good sensitivity and specificity.
The authors claim that they "used stringent (i.e., <= 25th percentile population norms on any of the 4 SF-36 scales) to define severe functional impairment". One of the SF-36 subscales in question is the "role emotional" subscale. This involves questions such as: "During the past 4 weeks, have you accomplished less than you would like as a result of any emotional problems?"
Does this really capture whether there has been a "substantial reduction in previous levels of .. personal activities"? [Full quote from paper[1]: 1) clinically evaluated, unexplained, persistent or relapsing chronic fatigue that is of new or definite onset [has not been lifelong]; is not the result of ongoing exertion; is not substantially alleviated by rest; and results in substantial reduction in previous levels of occupational, educational, social, or personal activities]
Perhaps the other three sub-scales cover this? For example, a better measure of whether the condition is having an effect on somebody's "personal activities" might be got from using the physical functioning subscales which asks about ability to walk distances, bath or dress oneself, etc. If this score is low, it's likely one's ability to do "personal activities" has been impaired.
Baraniuk[2] used the CDC '94 not operationalized in the same way as this study and found that CFS patients scores did have lower scores on some of the SF-36 subscales - but role emotional was one of the ones that weren't different (the others that weren't different were mental health and general health change).
Would it be possible for the authors to calculate the all important overall prevalence rate if those people who only satisfied this part of the "functional impairment" criteria are excluded? This data would be be useful not just in the US but around the world - countries around the world have been depending on the US to undertake such large scale (and expensive) studies on CFS.
Even before the recent broadening of the criteria, it had been felt by some that the CDC '94 criteria lacked specificity.
For example, Kennedy[3] investigated "patients with self-reported symptoms which developed sporadically (sCFS, n=48); after Gulf War service (GW, n=24); and following exposure to organophosphate insecticides (OP, n=25)" all of whom fulfilled the CDC '94 criteria[1]. Based on their findings, they concluded that "differences in simple, easily performed clinical outcome measurements can be observed between groups of patients, all of whom fulfill
the CDC-1994 criteria for CFS. It is likely that their response to treatment may also vary. The specificity of the CFS case definition should be improved to define more homogeneous groups of patients for the purposes of treatment and research."
Perhaps what is required is a totally new set of criteria?
Tom Kindlon
[1] Fukuda, K., Straus, S.E., Hickie, I., Sharpe, M.C., Dobbins, J.G., & Komaroff, A. (1994). The chronic fatigue syndrome: A comprehensive approach to its definition and study. Annals of Internal Medicine, 121 (12):953-959. http://www.annals.org/cgi/content/full/121/12/953
[2] James N Baraniuk, Begona Casado, Hilda Maibach, Daniel J Clauw, Lewis K Pannell and Sonja Hess S. A chronic fatigue syndrome - related proteome in human cerebrospinal fluid
[3] Kennedy G, Abbot NC, Spence V.A, Underwood C, Belch JJF. The specificity of the CDC-1994 criteria for chronic fatigue syndrome: comparison of health status in three groups of patients who fulfil the criteria. Ann Epidemiol 2004; 14: 95–100.
Competing interests
No competing interests
Does the use of the 'role emotional' subscale of the SF-36 help with sensitivty and specificity rates? Can we find out the prevalence rate if this subscale had not been used?
Sarah LaBelle, Chicago area CFIDS support group
18 June 2007
This paper presents results long awaited, prevalence of CFS beyond metropolitan areas. The huge difference in the metropolitan area rate of the Georgia study as compared to prior rates based on studies in other metropolitan areas is not well explained. The pre-publication discussion includes comment by the authors that this difference is not important, rather it is important that CFS is not diagnosed by simple physical test measurements.
The prevalence rate of this study is its single most important result. Huge variation needs more exploration of reasons why they occurred, and whether the result is reliable. Inclusion of the 'role emotional' subscale constitutes a substantial change in diagnostic method from prior work by the same lead author. The authors state they are using diagnostic approaches meant to improve the specificity of who is included as CFS, per the CDC 1994 criteria for CFS (1), which intention is applauded. However, 'role emotional' does not relate to any symptom in the listed criteria, directly or indirectly.
This has the effect of straying from the definition, perhaps broadening it, to include many who may be ill, but not with CFS.
The authors are correct in pointing out the difficulty in diagnosis for the purpose of research. The similarity in rate in two studies by different groups of researchers suggest the difficulty can be overcome by stringent application of the best tools at hand to include a person in the group with CFS. As the methods of this study are meant to be used in future studies of CFS, to standardize the study populations among various researchers, it is of great importance that the authors fully explore the effect of the new methods, and alter the methods if shown to decrease specificity.
Computing the prevalence rate without those changes to the criteria may reveal substantial differences in the prevalence rate for this specific disease, and explain the apparent change in rate of CFS. Can this further analysis be conducted, before other papers are published? These data should prove to be a rich vein of valuable information on CFS and the people who suffer from it. Those papers wil not be of much value on this shaky starting ground.
In short, I agree with the comments by Tom Kindlon, in calling for re-analysis of the rate based on these data, with changes to clong more rigidly to the published critieria. A ten-fold difference in prevalence is too large to ignore.
[1] Fukuda, K., Straus, S.E., Hickie, I., Sharpe, M.C., Dobbins, J.G., & Komaroff, A. (1994). The chronic fatigue syndrome: A comprehensive approach to its definition and study. Annals of Internal Medicine, 121 (12):953-959. http://www.annals.org/cgi/content/full/121/12/953
Competing interests
no competing interests
Questioning the use of the Role Emotional (RE) subscale of the SF-36 questionnaire in the diagnosis of CFS
Tom Kindlon, Irish ME/CFS Support Group
19 June 2007
As background to the previous two comments, I thought I'd point out that if people would like to see what makes up the Role Emotional (RE) subscale of the SF-36, a copy of a sample SF-36 questionnaire can be seen at: <http://www.nhlbi.nih.gov/resources/deca/wave/w11.pdf> .
It is question 6 i.e. 3 questions with only yes or no as possible answers.
The cut off point used in the current study is less than or equal to a score of 66 [1], so two "yes" answers (out of the three questions) is the cut off point for functional impairment.
Tom Kindlon
[1] Chronic Fatigue Syndrome – A clinically empirical approach to its definition and study.
William C Reeves, Dieter Wagner, Rosane Nisenbaum, James F Jones, Brian Gurbaxani, Laura Solomon, Dimitris A Papanicolaou, Elizabeth R Unger, Suzanne D Vernon and Christine Heim
BMC Medicine 2005, 3:19 doi:10.1186/1741-7015-3-19
<http://www.biomedcentral.com/1741-7015/3/19>
Competing interests
No competing interests
Whither Post-exertional Fatigue?
cort johnson, CFS Phoenix
21 June 2007
The Empirical Definition has many positive aspects; better characterization of CFS patients, a way to track treatment efficacy and perhaps identify symptom based subsets and it does appear to identify a very ill population. But does it single out the peculiar condition called CFS. Some aspects of it suggest to me that it does not.
Some researchers have proposed that post-exertional fatigue is a hallmark symptom in CFS. The Canadian Consensus and 1990 Australian definition require post-exertional fatigue to be present for a CFS diagnosis. The Fukuda definition does not; although it is one of eight major symptoms it is not required for a CFS diagnosis. The empirical definition appears to dilute the importance of this symptom further. Some evidence produced by CDC studies and others, however, suggests it is a central component of CFS.
A CDC study examining the symptoms in a wide variety of fatigued groups (prolonged fatigue, chronic fatigue, CFS-like, CFS) found that as the levels of fatigue increased the percentage of people reporting ‘unusual fatigue after exercise’ did as well (Nisenbaum 2006). That only 1.6% of people with no fatigue reported this symptom indicated it is rarely found in healthy people. (Problems with sleep, muscle and joint pain on the other hand were fairly common (10-20% of healthy people)). About 14% of people with prolonged fatigue and 33% with chronic fatigue reported unusual fatigue after exercise but from there the percentages jumped up markedly; 77 and 74% of CFS-like and CFS patients reported this symptom. This suggests there is a big difference between chronic fatigue patients (fatigued but don’t meet 1994 criteria for CFS) on the one hand and CFS-like (met the criteria but didn’t undergo the clinical evaluation) and CFS patients (meet the criteria, visited the clinic) with regard to this symptom.
Similarly CDC studies exploring the question of subsets in CFS (Conna et. al. 2006, Aslakson et. al. 2006) found that post-exertional fatigue – was the first and third most important differentiating variable in the PCA and Latent Class Analyses. Its discriminatory prowess was highlighted by the fact that it and concentration difficulties were the only variables not found at all in the Well Group. The very high levels of post exertional fatigue (78-91%) in the three classes dominated by CFS patients and the low to moderate levels of it (33-41%) in the classes dominated by idiopathic fatigue patients again indicated that this symptom plays a special role in CFS. CFS is often described as being an amalgam of very common symptoms but these studies indicate that post-exertional fatigue is only rarely found even a subset of the population one might expect it to; the BMI matched overweight, obese and even morbidly obese healthy controls in this study who presumably don’t exercise much.
Since the ‘chronic fatigue’ group in the Nisenbaum was the largest fatigued group studied in the Nisenbaum study (PF=575, CF=1085, CFS-like=263, CFS=43) this group will surely account for most of the increase in the prevalence rates under the empirical definition. This indicates that most CFS patients under the empirical definition will not be characterized by ‘unusual fatigue after exercise’. This is not in some ways surprising; Dr. White and Jason have pointed out patients can meet the new criteria for CFS simply by reporting they have low activity levels.
A Personal Response: For the first ten years after I got CFS I, who was formerly an avid exerciser, didn’t try to do anything more than walk. My symptoms at that point, while very disturbing, were nevertheless mostly not that unusual overall; I was very tired, I couldn’t concentrate well, my muscles hurt, I had constant sore throats, I felt out of it, I wasn’t strong. Basically I felt like I was shadow of my former self but I was able to get around, I was able to go to school. It probably could have been argued that I had some strange mental condition. Given the lack of information on CFS around that time – mid-1980’s, in the back of my mind I wondered if something like that had indeed occurred.
About 10 years into the disease I did something very unusual - I began an exercise program and have tried to do so several times since then. Each time my response was to it has been bizarre. The symptom exacerbation has been immense, not just at the beginning of the exercise program but throughout. Over time I was able to increase my strength and duration. In fact I usually felt good while I was exercising – but the aftermath was always devastating. Starting anywhere from ½ hour to several hours later I could feel that peculiar package of symptoms set in; the stiff, painful muscles, the heart yammering, the uncoordination, the need to lie down, the difficulty thinking or talking, the feelings of irritation. These symptoms would typically peak a day or so later and then slowly subside. It is an utterly strange response to exercise and it is the hallmark symptom of my CFS – it’s what convinced me that there was a physiological basis to my problems.
The idea that this vital part of CFS is being subsumed under this new definition suggests that while researchers may uncover important aspects of unwellness by studying this population they may very well have a very difficult time understanding the condition known as CFS.
Aslakson, E., Wollmer-Connar, U. and P. White. 2006. The validity of heterogeneity in chronic unexplained fatigue. Pharmacogenomics 7, 365-373
Conna, U., Aslakson, E. and P. White. 2006. An empirical delineation of the heterogeneity of chronic unexplained fatigue in women. Pharmacogenomics 7, 355-364.
Jason, Leonard. 2007. Problems with the new CDC CFS Prevalence Estimates. IACFS Website.
White, P. 2007. How common is chronic fatigue syndrome; how long is a piece of string? Population Health Metrics 5:6 doi:10.1186/1478-7954-5-6
Competing interests
none
Many possibilities to consider for metropolitan, urban, and rural differences in sex ratio.
Claire C., N/A
15 August 2007
One of the most interesting and potentially informative findings from this study is the finding that the gender ratio of CFS was strikingly different among metropolitan, urban, and rural populations.
The only suggestion that the authors make regarding this finding is that "The striking differences between female and male rates in the 3 strata may indicate risk effects of gender (a social construct) in distinction to sex (a biologic attribute)."
This is a very interesting suggestion, in light of all the research demonstrating that CFS is a physical disorder with biological markers. We should not fall under the line of thinking that medical observations whose causes are not yet explained are psychological or social constructs, or psychosomatic. This suggestion also assumes that gender constructs are different among metropolitan, urban, and rural populations.
There are many more obvious factors that are different among metropolitan, urban, and rural populations that should be investigated. Namely environmental factors including pollution, exposure to sunlight, microbes, and other things that may be different among metropolitan, urban, and rural populations.
There are many interesting studies which show that other illnesses such as multiple sclerosis have different prevalence rates by geography (latitude), and that asthma and allergies have different prevalence rates between urban and rural children. Could it be possible that the sexes have different levels of biological susceptibility to environmental triggers of some illnesses such as CFS?
Does the use of the "Role emotional" subscale of the SF-36 help with sensitivity and specificity rates? Can we find out the prevalence rate if this subscale hadn't been used?
15 June 2007
It is to be welcomed that attempts are being made to operationalize the CDC (94) CFS criteria [1], enabling easier comparisons between studies and making it easier for researchers to try to replicate findings.
So for example, having some sort of numerical value on a symptom so that one can say whether a symptom is present or not in a patient seems to be a good idea.
However if one is aiming to do this, it would seem preferable to choose methods that have good sensitivity and specificity rates for the condition in question. And it's questionnable whether the methods used in this study have good sensitivity and specificity.
The authors claim that they "used stringent (i.e., <= 25th percentile population norms on any of the 4 SF-36 scales) to define severe functional impairment". One of the SF-36 subscales in question is the "role emotional" subscale. This involves questions such as: "During the past 4 weeks, have you accomplished less than you would like as a result of any emotional problems?"
Does this really capture whether there has been a "substantial reduction in previous levels of .. personal activities"? [Full quote from paper[1]: 1) clinically evaluated, unexplained, persistent or relapsing chronic fatigue that is of new or definite onset [has not been lifelong]; is not the result of ongoing exertion; is not substantially alleviated by rest; and results in substantial reduction in previous levels of occupational, educational, social, or personal activities]
Perhaps the other three sub-scales cover this? For example, a better measure of whether the condition is having an effect on somebody's "personal activities" might be got from using the physical functioning subscales which asks about ability to walk distances, bath or dress oneself, etc. If this score is low, it's likely one's ability to do "personal activities" has been impaired.
Baraniuk[2] used the CDC '94 not operationalized in the same way as this study and found that CFS patients scores did have lower scores on some of the SF-36 subscales - but role emotional was one of the ones that weren't different (the others that weren't different were mental health and general health change).
Would it be possible for the authors to calculate the all important overall prevalence rate if those people who only satisfied this part of the "functional impairment" criteria are excluded? This data would be be useful not just in the US but around the world - countries around the world have been depending on the US to undertake such large scale (and expensive) studies on CFS.
Even before the recent broadening of the criteria, it had been felt by some that the CDC '94 criteria lacked specificity.
For example, Kennedy[3] investigated "patients with self-reported symptoms which developed sporadically (sCFS, n=48); after Gulf War service (GW, n=24); and following exposure to organophosphate insecticides (OP, n=25)" all of whom fulfilled the CDC '94 criteria[1]. Based on their findings, they concluded that "differences in simple, easily performed clinical outcome measurements can be observed between groups of patients, all of whom fulfill
the CDC-1994 criteria for CFS. It is likely that their response to treatment may also vary. The specificity of the CFS case definition should be improved to define more homogeneous groups of patients for the purposes of treatment and research."
Perhaps what is required is a totally new set of criteria?
Tom Kindlon
[1] Fukuda, K., Straus, S.E., Hickie, I., Sharpe, M.C., Dobbins, J.G., & Komaroff, A. (1994). The chronic fatigue syndrome: A comprehensive approach to its definition and study. Annals of Internal Medicine, 121 (12):953-959. http://www.annals.org/cgi/content/full/121/12/953
[2] James N Baraniuk, Begona Casado, Hilda Maibach, Daniel J Clauw, Lewis K Pannell and Sonja Hess S. A chronic fatigue syndrome - related proteome in human cerebrospinal fluid
BMC Neurology 2005, 5:22 doi:10.1186/1471-2377-5-22
http://www.biomedcentral.com/1471-2377/5/22
[3] Kennedy G, Abbot NC, Spence V.A, Underwood C, Belch JJF. The specificity of the CDC-1994 criteria for chronic fatigue syndrome: comparison of health status in three groups of patients who fulfil the criteria. Ann Epidemiol 2004; 14: 95–100.
Competing interests
No competing interests
Does the use of the 'role emotional' subscale of the SF-36 help with sensitivty and specificity rates? Can we find out the prevalence rate if this subscale had not been used?
18 June 2007
This paper presents results long awaited, prevalence of CFS beyond metropolitan areas. The huge difference in the metropolitan area rate of the Georgia study as compared to prior rates based on studies in other metropolitan areas is not well explained. The pre-publication discussion includes comment by the authors that this difference is not important, rather it is important that CFS is not diagnosed by simple physical test measurements.
The prevalence rate of this study is its single most important result. Huge variation needs more exploration of reasons why they occurred, and whether the result is reliable. Inclusion of the 'role emotional' subscale constitutes a substantial change in diagnostic method from prior work by the same lead author. The authors state they are using diagnostic approaches meant to improve the specificity of who is included as CFS, per the CDC 1994 criteria for CFS (1), which intention is applauded. However, 'role emotional' does not relate to any symptom in the listed criteria, directly or indirectly.
This has the effect of straying from the definition, perhaps broadening it, to include many who may be ill, but not with CFS.
The authors are correct in pointing out the difficulty in diagnosis for the purpose of research. The similarity in rate in two studies by different groups of researchers suggest the difficulty can be overcome by stringent application of the best tools at hand to include a person in the group with CFS. As the methods of this study are meant to be used in future studies of CFS, to standardize the study populations among various researchers, it is of great importance that the authors fully explore the effect of the new methods, and alter the methods if shown to decrease specificity.
Computing the prevalence rate without those changes to the criteria may reveal substantial differences in the prevalence rate for this specific disease, and explain the apparent change in rate of CFS. Can this further analysis be conducted, before other papers are published? These data should prove to be a rich vein of valuable information on CFS and the people who suffer from it. Those papers wil not be of much value on this shaky starting ground.
In short, I agree with the comments by Tom Kindlon, in calling for re-analysis of the rate based on these data, with changes to clong more rigidly to the published critieria. A ten-fold difference in prevalence is too large to ignore.
[1] Fukuda, K., Straus, S.E., Hickie, I., Sharpe, M.C., Dobbins, J.G., & Komaroff, A. (1994). The chronic fatigue syndrome: A comprehensive approach to its definition and study. Annals of Internal Medicine, 121 (12):953-959. http://www.annals.org/cgi/content/full/121/12/953
Competing interests
no competing interests
Questioning the use of the Role Emotional (RE) subscale of the SF-36 questionnaire in the diagnosis of CFS
19 June 2007
As background to the previous two comments, I thought I'd point out that if people would like to see what makes up the Role Emotional (RE) subscale of the SF-36, a copy of a sample SF-36 questionnaire can be seen at: <http://www.nhlbi.nih.gov/resources/deca/wave/w11.pdf> .
It is question 6 i.e. 3 questions with only yes or no as possible answers.
The cut off point used in the current study is less than or equal to a score of 66 [1], so two "yes" answers (out of the three questions) is the cut off point for functional impairment.
Tom Kindlon
[1] Chronic Fatigue Syndrome – A clinically empirical approach to its definition and study.
William C Reeves, Dieter Wagner, Rosane Nisenbaum, James F Jones, Brian Gurbaxani, Laura Solomon, Dimitris A Papanicolaou, Elizabeth R Unger, Suzanne D Vernon and Christine Heim
BMC Medicine 2005, 3:19 doi:10.1186/1741-7015-3-19
<http://www.biomedcentral.com/1741-7015/3/19>
Competing interests
No competing interests
Whither Post-exertional Fatigue?
21 June 2007
The Empirical Definition has many positive aspects; better characterization of CFS patients, a way to track treatment efficacy and perhaps identify symptom based subsets and it does appear to identify a very ill population. But does it single out the peculiar condition called CFS. Some aspects of it suggest to me that it does not.
Some researchers have proposed that post-exertional fatigue is a hallmark symptom in CFS. The Canadian Consensus and 1990 Australian definition require post-exertional fatigue to be present for a CFS diagnosis. The Fukuda definition does not; although it is one of eight major symptoms it is not required for a CFS diagnosis. The empirical definition appears to dilute the importance of this symptom further. Some evidence produced by CDC studies and others, however, suggests it is a central component of CFS.
A CDC study examining the symptoms in a wide variety of fatigued groups (prolonged fatigue, chronic fatigue, CFS-like, CFS) found that as the levels of fatigue increased the percentage of people reporting ‘unusual fatigue after exercise’ did as well (Nisenbaum 2006). That only 1.6% of people with no fatigue reported this symptom indicated it is rarely found in healthy people. (Problems with sleep, muscle and joint pain on the other hand were fairly common (10-20% of healthy people)). About 14% of people with prolonged fatigue and 33% with chronic fatigue reported unusual fatigue after exercise but from there the percentages jumped up markedly; 77 and 74% of CFS-like and CFS patients reported this symptom. This suggests there is a big difference between chronic fatigue patients (fatigued but don’t meet 1994 criteria for CFS) on the one hand and CFS-like (met the criteria but didn’t undergo the clinical evaluation) and CFS patients (meet the criteria, visited the clinic) with regard to this symptom.
Similarly CDC studies exploring the question of subsets in CFS (Conna et. al. 2006, Aslakson et. al. 2006) found that post-exertional fatigue – was the first and third most important differentiating variable in the PCA and Latent Class Analyses. Its discriminatory prowess was highlighted by the fact that it and concentration difficulties were the only variables not found at all in the Well Group. The very high levels of post exertional fatigue (78-91%) in the three classes dominated by CFS patients and the low to moderate levels of it (33-41%) in the classes dominated by idiopathic fatigue patients again indicated that this symptom plays a special role in CFS. CFS is often described as being an amalgam of very common symptoms but these studies indicate that post-exertional fatigue is only rarely found even a subset of the population one might expect it to; the BMI matched overweight, obese and even morbidly obese healthy controls in this study who presumably don’t exercise much.
Since the ‘chronic fatigue’ group in the Nisenbaum was the largest fatigued group studied in the Nisenbaum study (PF=575, CF=1085, CFS-like=263, CFS=43) this group will surely account for most of the increase in the prevalence rates under the empirical definition. This indicates that most CFS patients under the empirical definition will not be characterized by ‘unusual fatigue after exercise’. This is not in some ways surprising; Dr. White and Jason have pointed out patients can meet the new criteria for CFS simply by reporting they have low activity levels.
A Personal Response: For the first ten years after I got CFS I, who was formerly an avid exerciser, didn’t try to do anything more than walk. My symptoms at that point, while very disturbing, were nevertheless mostly not that unusual overall; I was very tired, I couldn’t concentrate well, my muscles hurt, I had constant sore throats, I felt out of it, I wasn’t strong. Basically I felt like I was shadow of my former self but I was able to get around, I was able to go to school. It probably could have been argued that I had some strange mental condition. Given the lack of information on CFS around that time – mid-1980’s, in the back of my mind I wondered if something like that had indeed occurred.
About 10 years into the disease I did something very unusual - I began an exercise program and have tried to do so several times since then. Each time my response was to it has been bizarre. The symptom exacerbation has been immense, not just at the beginning of the exercise program but throughout. Over time I was able to increase my strength and duration. In fact I usually felt good while I was exercising – but the aftermath was always devastating. Starting anywhere from ½ hour to several hours later I could feel that peculiar package of symptoms set in; the stiff, painful muscles, the heart yammering, the uncoordination, the need to lie down, the difficulty thinking or talking, the feelings of irritation. These symptoms would typically peak a day or so later and then slowly subside. It is an utterly strange response to exercise and it is the hallmark symptom of my CFS – it’s what convinced me that there was a physiological basis to my problems.
The idea that this vital part of CFS is being subsumed under this new definition suggests that while researchers may uncover important aspects of unwellness by studying this population they may very well have a very difficult time understanding the condition known as CFS.
Aslakson, E., Wollmer-Connar, U. and P. White. 2006. The validity of heterogeneity in chronic unexplained fatigue. Pharmacogenomics 7, 365-373
Conna, U., Aslakson, E. and P. White. 2006. An empirical delineation of the heterogeneity of chronic unexplained fatigue in women. Pharmacogenomics 7, 355-364.
Jason, Leonard. 2007. Problems with the new CDC CFS Prevalence Estimates. IACFS Website.
White, P. 2007. How common is chronic fatigue syndrome; how long is a piece of string? Population Health Metrics 5:6 doi:10.1186/1478-7954-5-6
Competing interests
none
Many possibilities to consider for metropolitan, urban, and rural differences in sex ratio.
15 August 2007
One of the most interesting and potentially informative findings from this study is the finding that the gender ratio of CFS was strikingly different among metropolitan, urban, and rural populations.
The only suggestion that the authors make regarding this finding is that "The striking differences between female and male rates in the 3 strata may indicate risk effects of gender (a social construct) in distinction to sex (a biologic attribute)."
This is a very interesting suggestion, in light of all the research demonstrating that CFS is a physical disorder with biological markers. We should not fall under the line of thinking that medical observations whose causes are not yet explained are psychological or social constructs, or psychosomatic. This suggestion also assumes that gender constructs are different among metropolitan, urban, and rural populations.
There are many more obvious factors that are different among metropolitan, urban, and rural populations that should be investigated. Namely environmental factors including pollution, exposure to sunlight, microbes, and other things that may be different among metropolitan, urban, and rural populations.
There are many interesting studies which show that other illnesses such as multiple sclerosis have different prevalence rates by geography (latitude), and that asthma and allergies have different prevalence rates between urban and rural children. Could it be possible that the sexes have different levels of biological susceptibility to environmental triggers of some illnesses such as CFS?
Competing interests
None