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Replication of an empirical approach to delineate the heterogeneity of chronic unexplained fatigue

Discussion in 'Latest ME/CFS Research' started by Tom Kindlon, Apr 15, 2014.

  1. Tom Kindlon

    Tom Kindlon Senior Member

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    I'm not a fan of this paper but wanted to post the comments in message #2 (from 2009) somewhere

    Free full text: http://www.pophealthmetrics.com/content/7//17

  2. Tom Kindlon

    Tom Kindlon Senior Member

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    Some comments on this (originally written in 2009)
    ----
    I thought I'd say that if one only reads some papers on CFS, I'd put this one into the bundle of ones of low priority to read!

    They analysed the data of the women of the Georgia cohort including the healthy people and unwell people who didn't have CFS [so only 92 (23.8%) have CFS out of 386 and we are talking empirical definition (Reeves, 2005) so perhaps only 7-25 (out of 386!) "really" have CFS].

    The main analysis came up with five classes (they did another analysis which came up with four classes and we are really not given much information on these four classes even though they are discussed now and then).

    Nearly all of the CFS patients are in classes 1 (44%) or 2 (51%) (in the five class solution). 3% are in class 3, 1% are in class 4 and 0% are in class 5.

    So if interested in heterogeneity with regard to CFS, you are interested in the differences between classes 1 and 2.

    It is of course not an ideal way to look at heterogeneity with regard to CFS as the CFS patients only make up 41/97 (42.3%) of class 1 and 47/92 (51.1%) of class 2.

    Here are the descriptions for classes 1 and 2 (remember that not all have CFS and this is the empirical definition) (from Table 7):

    Class 1: polysymptomatic, depressed, insomnia, not obese
    Class 2: polysymptomatic, depressed, insomnia, Obese, metabolic strain

    Anyone notice the similarities and differences?

    Similarities: polysymptomatic, depressed, insomnia

    Differences: "not obese" vs "Obese, metabolic strain"

    Here is another set of descriptions from the text: "Class 1 (25%) captured ill subjects with many symptoms, prominent fatigue, sleep problems, and depression, but no aberrant biological markers (including body mass index) characterized this group. Class 2 (24%) similarly captured ill subjects who reported prominent, widespread symptoms, insomnia, and depression. However, these subjects had an associated metabolic syndrome (elevated insulin and inflammatory markers) and were obese."

    One can see from the pre-publication comments that in the original draft the authors said: "The replication of heterogeneity found in an independent population derived sample provides the strongest support yet published of the heterogeneous nature of CFS."

    Not surprisingly, a reviewer told them to tone this down.

    I might as well make one point here even though I also intend to make it as a comment:

    They keep saying that it shows that the research shows that depression needs to be used to stratify CFS patients. But the two classes with virtually all the CFS patients (96%) had comparable levels of depression!

    The authors make all sorts of other comments about what their study shows about CFS. But really it doesn't show very much as there are virtually no CFS patients in Classes 3-5 and around half the people in classes 1 and 2 don't have CFS. And as I say, Classes 1 and 2 aren't that different.

    And of course CFS is defined using the empirical definition so lots wouldn't normally be said to have CFS at all!
    Esther12, Simon, Sean and 2 others like this.
  3. Tom Kindlon

    Tom Kindlon Senior Member

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  4. biophile

    biophile Places I'd rather be.

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    At first it didn't make sense that there is no class for polysymptomatic, insomnia, not obese, not depressed. The SCID is mentioned, but it is not clear how they defined "depressed mood", it is possible that physical symptoms counted towards "depressed mood". However, it made perfect sense once realizing that it used the CDC's "empirical" definition of CFS, which was notorious for increasing the prevalence estimates by 10-fold, including or conflating with primary major depression rather than primary CFS, and allowing emotional problems to fulfill the limitations requirement without physical problems?
    Last edited: Apr 16, 2014
    Esther12, Tom Kindlon and Valentijn like this.

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