Defining the minimally clinically important difference of the SF-36 physical function subscale for paediatric CFS/ME - Crawley et al

Sly Saint

Sly Saint

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Defining the minimally clinically important difference of the SF-36 physical function subscale for paediatric CFS/ME: triangulation using three different methods

  • Amberly Brigden
  • Roxanne M Parslow
  • Daisy Gaunt
  • Simon M Collin
  • Andy Jones
  • Esther Crawley


Abstract
Background

Defining the minimally clinically important difference (MCID) is important for the design and analysis of clinical trials and ensures that findings are clinically meaningful. Studies in adult populations have investigated the MCID of The Short Form 36 physical function sub-scale (SF-36-PFS). However, to our knowledge no studies have defined the MCID of the SF-36-PFS in a paediatric population. We aimed to triangulate findings from distribution, anchor and qualitative methods to identify the MCID of the SF-36-PFS for children and adolescents with CFS/ME.

Methods
Quantitative methods: We analysed routinely-collected data from a specialist paediatric CFS/ME service in South-West England using: 1) the anchor method, based on Clinical Global Impression (CGI) outcomes at 6 months’ follow-up; 2) the distribution method, based on the standard deviation of baseline SF-36-PFS scores.

Qualitative methods: Young people (aged 12–17 years) and parents were asked to complete the SF-36-PFS, marking each question twice: once for where they would currently rate themselves/their child and a second time to show what they felt would be the smallest amount of change for them/their child to feel treatment had made a difference. Semi-structured interviews were designed to explore what factors were deemed important to patients and to what extent an improvement was considered satisfactory. We thematically analysed qualitative interviews from 21 children and their parents.

Results
Quantitative results: Six-month follow-up data were available for 198 children with a mean age of 14 years. Most were female (74%, 146/198) and 95% gave their ethnicity as “White British”.

Half the standard deviation of the baseline SF-36-PFS scores was 11.0. “A little better” on the CGI equated to a mean difference on the SF-36-PFS from baseline to 6-month follow-up of 9.0.

Qualitative results: Twenty-one children with CFS/ME participated: 16 females (76.2%) with a mean age of 14.4 years. Twenty mothers and two fathers were also interviewed.

The median minimal improvement in the SF-36-PFS was 10. Participants indicated that small changes in physical function can lead to important improvements in valued social and family function. Patients and parents were positive about improvement even in the presence of persisting symptoms.

Triangulation: The MCID based on the mean score from the three methods was 10.

Conclusions
Converging evidence indicates future studies in paediatric CFS/ME should use an MCID of 10 on the SF-36-PFS.

Keywords
Minimal clinically important difference (MCID) Paediatric Chronic fatigue syndrome Myalgic encephalomyelitis CFS/ME
Abbreviations
CFS/ME
Chronic Fatigue Syndrome / Myalgic Encephalomyelitis

CGI
Clinical Global Impression Scale

MCID
Minimal Clinically Important Difference

SF-36-PFS
The SF-36 physical function sub-scale
https://doi.org/10.1186/s12955-018-1028-2) contains supplementary material, which is available to authorized users.
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https://link.springer.com/article/10.1186/s12955-018-1028-2
 
NOTE: I'm unusually sleep deprived, so this may be nonsense.

"Ethics approval and consent to participate
Qualitative data: Full ethical approval was obtained from the NRES Committee North West (08/04/2014, ref 14/NW/0170). An amendment to use one-to-one interviews with children, parents and clinicians who are unable to attend focus groups and to include exploration of important outcomes was approved (21/10/2014, ref 14/NW/0770). Relevant R&D approval was obtained from the RNHRD (20/06/2014, ref-RBB 427).

Quantitative data: The quantitative data was collected routinely as part of service evaluation. The North Somerset & South Bristol Research Ethics Committee determined that collection and analysis of these CFS/ME patient data did not require ethical review by an NHS Research Ethics Committee or approval by NHS Research and Development offices (REC ref. 07/Q2006/48)."

Looks like they did also get ethics approval for interviews this time, so maybe this doesn't matter, but re the Quantitative data, isn't that the same code @dave30th has written about being misused elsewhere?

re this study: Looks like they're just relying on subjective self-report outcomes, rather than assessing what level of change in SF36-PF was reliably associated with a significant improvement in some objective outcome, like actometers. I also couldn't see any reference to them having explained potential problems with thigs like response bias to the participants who were giving their views on what a MCID would be. So this study is of no value for deciding what should be viewed as a MCID in the sort of nonblinded trials Crawley has been conducting.

Data were used from a larger qualitative study exploring how “recovery” should be measured in paediatric CFS/ME
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Can Crawley's team get patients to validate her past spin!

A section of the semi-structured topic guide (lasting 30–45 min) included questions on the MCID; young people and their parent/carers were asked open-ended questions designed to explore what they considered the smallest change on each item of the SF-36-PFS to be subjectively meaningful. During the semi-structured interview, children were asked to complete the SF-36-PFS. Participants were asked to mark each question twice: once for where they would currently rate themselves and a second time to show what they felt would be the smallest amount of change for them to feel treatment had made a difference which was worth having treatment for. Parents/carers were also asked to complete this process; to mark their child’s current health status and then provide a second mark to indicate the smallest amount of change to feel like treatment has made a difference for their child. See Additional file 1 for the topic guide.
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Wouldn't this depend on what the treatment was, and how much effort it was?

During discussions, participants emphasised the importance of basic mobility as a marker of meaningful improvement. Participants typically felt walking (100 yards or half a mile) and climbing one flight of stairs was important as this level of mobility was seen as necessary for the basic and essential daily tasks like being able to move around their own home.
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I guess it's obvious that they'd value different items very differently, but doesn't that make the idea they they've endorsed a MCID of 10 difficult to justify? It sounds like it really depends on which two items improved. The way they phrased things in the quote before last would mean that participants will have been encouraged to choose the two items that they valued more than any other, whereas an MCID of 10 would mean that improvement in any two items would be seen as a MCID.

This is a tiny bit interesting, but would be so much more interesting if they'd looked at correlations with an objective outcome:

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I don't think this paper contributes much. An MCID of 10 in a rigorously conducted double-blind trial sounds reasonable (although this paper actually makes me think that many children with CFS would only agree if the change came from their prioritised items). This paper provides no reason to think that a change of 10 indicates a clinically significant difference in nonblinded trials where participants in one arm were encouraged to adopt positive views about their treatment or health.
 
I just got re-annoyed about this study, but that's possibly because I'm sleep deprived.

Is it just me, or does it look as if they just wanted to do a science-looking experiment, rather than get more useful information by just asking kids what they thought should be the MCID?

During the semi-structured interview, children were asked to complete the SF-36-PFS. Participants were asked to mark each question twice: once for where they would currently rate themselves and a second time to show what they felt would be the smallest amount of change for them to feel treatment had made a difference which was worth having treatment for.
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As they note, kids value changes in different items very differently, so their experiment is likely to lead to a lower MCID than if they'd just explained to kids what an MCID was used for, and then asked them what they thought a good MCID would be.

They set up this 'experiment' so that every child will have been using the items that they most valued change on to set the MCID. It could be that if the kids involved had been asked what change should be used to estimate a MCID in clinical trials or observational studies, when an MCID of 10 would mean improvement for any two items and it should not be assumed that the first two to change will be the two most valued by the patient, that they'd have thought an MCID of greater than 10 would be appropriate.

I don't understand why they'd do things the way they did, unless they just wanted to make that bit look a bit more 'sciencey' than a poll of 21 kids.
 
Esther12 said:
I am worried that Crawley (and others like her) are training up PhD students to do cargo-cult science that lets them get a career but contributes nothing to society.
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That worries me too. The next generation being brainwashed and formed into the next cabal to cite and review each others papers and destroy more sick people's lives.
 
Sorry for the necro. Do we have any reliable studies showing MCID/MID for the major symptom questionnaires currently in use? For instance, for the De Paul Symptom Questionnaire.
 
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