On 2015 Aug 17, Alem Matthees commented:

In response to post-publication feedback, I wish to clarify some aspects of the abstract, so there are no further misunderstandings about the scope and content in the full text of this article:

a) Classification and naming issues aside, ME/CFS occurs at all ages, including young children and adolescents. [1] I never intended to suggest otherwise. The statement about patients being almost exclusively of working age was in context of research cohorts, particularly intervention trials which typically exclude patients under 18 years of age and rarely recruit those over 65 years. It is argued that studies consisting of such cohorts should not use normative data from general populations which include the elderly.

b) The physical function subscale of the Short Form 36 health survey (PF SF-36) is discussed because it is a commonly used measure in research and was used in the PACE trial. This article is not a defence of the PACE trial, but uses it to exemplify how the issues described earlier in the article can cause normative data to be misinterpreted or misapplied. Selected details on this issue can be found in an BMJ Rapid Response (open-access) which does not require subscription to view. [2]

c) This article is not meant to be a comprehensive analysis of recovery or case definitions, it is simply a commentary which focuses on using normative data from other comparison groups, one of the issues raised in the review by Adamowicz et al. [3] It explores the appropriate control groups or comparison populations, highlights a problem with using the mean ±1 SD as a threshold if the data does not follow a normal distribution, includes some summary statistics, mentions statistical testing at the group level, and encourages researchers to publish enough information so that others can accurately estimate the functional status of participants. Subjective self-reported measures are important but have potential biases (particularly in nonblinded trials lacking placebo control). Objective measures are also important, particularly when assertions that the intervention is effective at increasing function and activity are contradicted by a range of objective measures. See commentaries by Twisk [4] and others. [5-7]

References

1: Bakken IJ, Tveito K, Gunnes N, Ghaderi S, Stoltenberg C, Trogstad L, Håberg SE, Magnus P. Two age peaks in the incidence of chronic fatigue syndrome/myalgic encephalomyelitis: a population-based registry study from Norway 2008-2012. BMC Med. 2014 Oct 1;12:167. doi: 10.1186/s12916-014-0167-5. PMID 25274261. http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/25274261

2: Matthees A. Re: Tackling fears about exercise is important for ME treatment, analysis indicates. BMJ Rapid Response, 21 January 2015. http://www.bmj.com/content/350/bmj.h227/rr-16

3: Adamowicz JL, Caikauskaite I, Friedberg F. Defining recovery in chronic fatigue syndrome: a critical review. Qual Life Res. 2014 Nov;23(9):2407-16. doi: 10.1007/s11136-014-0705-9. Epub 2014 May 3. PMID: 24791749. http://link.springer.com/article/10.1007/s11136-014-0705-9

4: Twisk FN. A definition of recovery in myalgic encephalomyelitis and chronic fatigue syndrome should be based upon objective measures. Qual Life Res. 2014 Nov;23(9):2417-8. doi: 10.1007/s11136-014-0737-1. Epub 2014 Jun 17. PMID: 24935018. http://link.springer.com/article/10.1007/s11136-014-0737-1

5: Kindlon TP. Objective measures found a lack of improvement for CBT & GET in the PACE Trial: subjective improvements may simply represent response biases or placebo effects in this non-blinded trial. BMJ Rapid Response, 18 January 2015. http://www.bmj.com/content/350/bmj.h227/rr-10

6: Wilshire CE. Re: Tackling fears about exercise is important for ME treatment, analysis indicates. BMJ Rapid Response, 19 January 2015. http://www.bmj.com/content/350/bmj.h227/rr-7

7: Faulkner G. In non-blinded trials, self-report measures could mislead. Lancet Psychiatry. Volume 2, No. 4, e7, April 2015. doi: 10.1016/S2215-0366(15)00089-9 http://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(15)00089-9/fulltext

On 2015 Aug 17, Alem Matthees commented:

In response to post-publication feedback, I wish to clarify some aspects of the abstract, so there are no further misunderstandings about the scope and content in the full text of this article:

a) Classification and naming issues aside, ME/CFS occurs at all ages, including young children and adolescents. [1] I never intended to suggest otherwise. The statement about patients being almost exclusively of working age was in context of research cohorts, particularly intervention trials which typically exclude patients under 18 years of age and rarely recruit those over 65 years. It is argued that studies consisting of such cohorts should not use normative data from general populations which include the elderly.

b) The physical function subscale of the Short Form 36 health survey (PF SF-36) is discussed because it is a commonly used measure in research and was used in the PACE trial. This article is not a defence of the PACE trial, but uses it to exemplify how the issues described earlier in the article can cause normative data to be misinterpreted or misapplied. Selected details on this issue can be found in an BMJ Rapid Response (open-access) which does not require subscription to view. [2]

c) This article is not meant to be a comprehensive analysis of recovery or case definitions, it is simply a commentary which focuses on using normative data from other comparison groups, one of the issues raised in the review by Adamowicz et al. [3] It explores the appropriate control groups or comparison populations, highlights a problem with using the mean ±1 SD as a threshold if the data does not follow a normal distribution, includes some summary statistics, mentions statistical testing at the group level, and encourages researchers to publish enough information so that others can accurately estimate the functional status of participants. Subjective self-reported measures are important but have potential biases (particularly in nonblinded trials lacking placebo control). Objective measures are also important, particularly when assertions that the intervention is effective at increasing function and activity are contradicted by a range of objective measures. See commentaries by Twisk [4] and others. [5-7]

References

1: Bakken IJ, Tveito K, Gunnes N, Ghaderi S, Stoltenberg C, Trogstad L, Håberg SE, Magnus P. Two age peaks in the incidence of chronic fatigue syndrome/myalgic encephalomyelitis: a population-based registry study from Norway 2008-2012. BMC Med. 2014 Oct 1;12:167. doi: 10.1186/s12916-014-0167-5. PMID 25274261. http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/25274261

2: Matthees A. Re: Tackling fears about exercise is important for ME treatment, analysis indicates. BMJ Rapid Response, 21 January 2015. http://www.bmj.com/content/350/bmj.h227/rr-16

3: Adamowicz JL, Caikauskaite I, Friedberg F. Defining recovery in chronic fatigue syndrome: a critical review. Qual Life Res. 2014 Nov;23(9):2407-16. doi: 10.1007/s11136-014-0705-9. Epub 2014 May 3. PMID: 24791749. http://link.springer.com/article/10.1007/s11136-014-0705-9

4: Twisk FN. A definition of recovery in myalgic encephalomyelitis and chronic fatigue syndrome should be based upon objective measures. Qual Life Res. 2014 Nov;23(9):2417-8. doi: 10.1007/s11136-014-0737-1. Epub 2014 Jun 17. PMID: 24935018. http://link.springer.com/article/10.1007/s11136-014-0737-1

5: Kindlon TP. Objective measures found a lack of improvement for CBT & GET in the PACE Trial: subjective improvements may simply represent response biases or placebo effects in this non-blinded trial. BMJ Rapid Response, 18 January 2015. http://www.bmj.com/content/350/bmj.h227/rr-10

6: Wilshire CE. Re: Tackling fears about exercise is important for ME treatment, analysis indicates. BMJ Rapid Response, 19 January 2015. http://www.bmj.com/content/350/bmj.h227/rr-7

7: Faulkner G. In non-blinded trials, self-report measures could mislead. Lancet Psychiatry. Volume 2, No. 4, e7, April 2015. doi: 10.1016/S2215-0366(15)00089-9 http://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(15)00089-9/fulltext