Tag: Oxford criteria

Myalgic encephalomyelitis/chronic fatigue Syndrome (ME/CFS): Investigating care practices pointed out to disparities in diagnosis and treatment across European Union

Abstract:

ME/CFS is a chronic, complex, multisystem disease that often limits the health and functioning of the affected patients. Diagnosing patients with ME/CFS is a challenge, and many different case definitions exist and are used in clinical practice and research. Even after diagnosis, medical treatment is very challenging. Symptom relief and coping may affect how patients live with their disease and their quality of life. There is no consensus on which diagnostic criteria should be used and which treatment strategies can be recommended for patients.

The purpose of the current project was to map the landscape of the Euromene countries in respect of national guidelines and recommendations for case definition, diagnosis and clinical approaches for ME/CFS patients. A 23 items questionnaire was sent out by email to the members of Euromene. The form contained questions on existing guidelines for case definitions, treatment/management of the disease, tests and questionnaires applied, and the prioritization of information for data sampling in research. We obtained information from 17 countries. Five countries reported having national guidelines for diagnosis, and five countries reported having guidelines for clinical approaches.

For diagnostic purposes, the Fukuda criteria were most often recommended, and also the Canadian Consensus criteria, the International Consensus Criteria and the Oxford criteria were used. A mix of diagnostic criteria was applied within those countries having no guidelines. Many different questionnaires and tests were used for symptom registration and diagnostic investigation. For symptom relief, pain and anti-depressive medication were most often recommended. Cognitive Behavioral Therapy and Graded Exercise treatment were often recommended as disease management and rehabilitative/palliative strategies.

The lack of consistency in recommendations across European countries urges the development of regulations, guidance and standards. The results of this study will contribute to the harmonization of diagnostic criteria and treatment for ME/CFS in Europe.

Source: Strand EB, Nacul L, Mengshoel AM, Helland IB, Grabowski P, Krumina A, Alegre-Martin J, Efrim-Budisteanu M, Sekulic S, Pheby D, Sakkas GK, Sirbu CA, Authier FJ; European Network on ME/CFS (EUROMENE). Myalgic encephalomyelitis/chronic fatigue Syndrome (ME/CFS): Investigating care practices pointed out to disparities in diagnosis and treatment across European Union. PLoS One. 2019 Dec 5;14(12):e0225995. doi: 10.1371/journal.pone.0225995. eCollection 2019. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0225995 (Full article)

Chronic Fatigue Syndrome prevalence is grossly overestimated using Oxford criteria compared to Centers for Disease Control (Fukuda) criteria in a U.S. population study

Abstract:

BACKGROUND: Results from treatment studies using the low threshold Oxford criteria for recruitment may have been overgeneralized to patients diagnosed by more stringent CFS criteria.

PURPOSE: To compare the selectivity of Oxford and Fukuda criteria in a U.S. population.

METHODS: Fukuda (Center for Disease Control (CDC)) criteria, as operationalized with the CFS Severity Questionnaire (CFSQ), were included in the nationwide rc2004 HealthStyles survey mailed to 6,175 participants who were representative of the US 2003 Census population. The 9 questionnaire items (CFS symptoms) were crafted into proxies for Oxford criteria (mild fatigue, minimal exclusions) and Fukuda criteria (fatigue plus ≥4 of 8 ancillary criteria at moderate or severe levels with exclusions). The comparative prevalence estimates of CFS were then determined. Severity scores for fatigue were plotted against the sum of severities for the 8 ancillary criteria. The 4 quadrants of scatter diagrams assessed putative healthy controls, CFS, chronic idiopathic fatigue, and CFS-like with insufficient fatigue subjects.

RESULTS: The Oxford criteria designated CFS in 25.5% of 2,004 males and 19.9% of 1,954 females. Based on quadrant analysis, 85% of Oxford-defined cases were inappropriately classified as CFS. Fukuda criteria identified CFS in 2.3% of males and 1.8% of females.

DISCUSSION: CFS prevalence using Fukuda criteria and quadrant analysis were near the upper limits of previous epidemiology studies. The CFSQ may have utility for on-line and outpatient screening. The Oxford criteria were untenable because they inappropriately selected healthy subjects with mild fatigue and chronic idiopathic fatigue and mislabeled them as CFS.

Source: Baraniuk JN. Chronic Fatigue Syndrome prevalence is grossly overestimated using Oxford criteria compared to Centers for Disease Control (Fukuda) criteria in a U.S. population study. Fatigue. 2017;5(4):215-230. doi: 10.1080/21641846.2017.1353578. Epub 2017 Jul 21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6407870/ (Full article)

Neurometabolites in anterior cingulate cortex in chronic fatigue syndrome: A magnetic resonance spectroscopy study at 7 Tesla

Abstract:

Background: Chronic fatigue syndrome (CFS) is a disorder characterized by prolonged physical and mental fatigue that cannot be explained by another established medical diagnosis. The anterior cingulate cortex (ACC) and putamen are two regions involved in frontal-striatal neural circuitry, which may be related to the pathophysiology of CFS. The aim of this study was to investigate the concentrations of neurometabolites, including glutamate, gamma-aminobutyric acid (GABA) and glutathione, in the ACC and putamen, using magnetic resonance spectroscopy (MRS) at 7 Tesla (7T). In addition, this study also aimed to evaluate resting-state functional connectivity in CFS with functional magnetic resonance imaging (fMRI).

Methods: This study involved 12 patients who met the Oxford criteria for CFS and 25 healthy controls. Participants rated themselves on the Chalder Fatigue Questionnaire (CFQ) and the Beck Depression Inventory (BDI). All participants had a single proton (1H) MRS and resting-state fMRI scan with a 7T Siemens MAGNETOM scanner (Siemens, Erlangen, Germany) with a Nova Medical 32 channel receive array head coil. Spectra were measured from voxels in the ACC (20 × 20 × 20 mm), putamen (10 × 16 × 20 mm) and occipital cortex (20 × 20 × 20 mm). Spectra were analysed with LCModel to obtain absolute concentrations of the neurochemicals. Differences in functional connectivity between CFS and healthy participants were tested using multivariate exploratory linear optimized decomposition into independent components (MELODIC) and dual regression.

Results: Concentrations of putamen glutamate and glutamate+glutamine (Glx) were increased in CFS while that of ACC GABA was decreased. Putamen Glx and ACC glutamine were negatively associated with the severity of self-reported fatigue. There were main effects of CFS diagnosis on glutathione (GSH) and total creatine, indicating decreases of these neurometabolites in all the regions studied in CFS patients. In addition, the CFS patients demonstrated elevated functional connectivity between the default mode network and right supracalcarine cortex, precuneus cortex and dorsolateral prefrontal cortex.

Conclusions: The increased putamen glutamate, decreased ACC GABA and elevated resting state functional connectivity of the default mode network suggest a hyperactive brain status in CFS. The global decrease of GSH and total creatine also suggest that CFS patients may have an abnormal bioenergetic status with higher oxidative stress.

Source: Chi Chen. Neurometabolites in anterior cingulate cortex in chronic fatigue syndrome: A magnetic resonance spectroscopy study at 7 Tesla. Oxford University Research Archive. September 22, 2017. (Open access article) https://ora.ox.ac.uk/objects/uuid:60ff242e-2ccd-4f23-ac7d-16553d864e8b

The role of IP-10 in Chronic Fatigue Syndrome

Abstract:

Chronic fatigue syndrome (CFS) is a severely debilitating and complex illness of uncertain cause, characterised by prolonged, fatigue triggered by minimal activity. There is evidence that CFS is associated with chronic inflammation. Studies have shown that plasma levels of cytokines are chronically modified in patients with CFS.

This study examined physiological, subjective and cognitive factors associated with plasma cytokine concentrations in a cohort of 92 patients compared with age and sex matched healthy controls. A sub-group of patients and healthy controls (HCs) also underwent more detailed analyses of muscle function, cytokine production and cognitive function. Patients were diagnosed with CFS if they met the Oxford criteria for Chronic Fatigue Syndrome and recommended NICE guidelines. Patients completed a number of validated questionnaires including the Chalder Fatigue Questionnaire (CFQ) which is considered a valid and reliable measure of fatigue in patients with CFS.

Patients with CFS demonstrated a characteristic significant reduction in Maximal Voluntary Contraction Force compared with HCs. Data on plasma concentrations of 27 pro- and anti-inflammatory cytokines were analysed using multiple or logistic regression with age and sex which were significant covariates included in each model. CFS was strongly associated with a limited number of cytokines. Diagnosis of CFS was associated with increased plasma contents of MIP-1a, MIP-1b and RANTES (p<0.05) and marginally with Eotaxin (p=0.07) when modelled individually. MVC and self-reported fatigue both showed particularly strong associations with plasma IP-10 concentrations.

Muscle content of IP-10 mRNA was significantly elevated, suggesting that, at least in part, muscle was a source of this IP-10 but not the other cytokines. Pairwise associations between MVC and cytokines demonstrated that the reduced MVC seen in patients with CFS was strongly associated with plasma levels of IP-10, TNF-α and IL-5. Further analyses revealed strong correlations between plasma RANTES and eotaxin levels and poorer verbal recall and RTs of patients with CFS. The consistent association of IP-10 with the physiological features and of RANTES and eotaxin with the cognitive features of CFS provides compelling evidence for a role of these cytokine/chemokines in the physiological and cognitive pathology of CFS.

This work was funded by the Medical Research Council.

Source: Anne McArdle, Arief Gusnanto, Kate Earl, George Sakellariou, Clare Lawton, Daniel Owens, Graeme Close, Michael Beadsworth and Louise Dye. The role of IP-10 in Chronic Fatigue Syndrome. April 2017, The FASEB Journal, vol. 31 no. 1 Supplement lb789. http://www.fasebj.org/content/31/1_Supplement/lb789.short

 

Mediators of the effects on fatigue of pragmatic rehabilitation for chronic fatigue syndrome

Abstract:

OBJECTIVE: To examine potential mediators of the effect of pragmatic rehabilitation on improvements in fatigue following a randomized controlled trial for patients with chronic fatigue syndrome (CFS/ME) in primary care (IRCTN 74156610).

METHOD: Patients fulfilled the Oxford criteria for CFS. Ninety-five patients were randomized to pragmatic rehabilitation and 100 to general practitioner (GP) treatment as usual. The outcome was the Chalder fatigue scale score (0123 scoring) at end of treatment (20 weeks) and 1-year follow up (70 weeks). First, the effect of treatment on potential mediators was assessed. Then fatigue was regressed on significant mediators, treatment allocation, and baseline measures of fatigue and significant mediators.

RESULTS: Reduction in limiting activities at 20 weeks mediated the positive effect of pragmatic rehabilitation on fatigue at 70 weeks (mediated effect size = -2.64, SE = 0.81, p = .001, proportion of effect mediated = 82.0%). Reduction in catastrophizing at 20 weeks mediated the positive effect of pragmatic rehabilitation on fatigue at 70 weeks (mediated effect size = -1.39, SE = 0.61, p = .023, proportion of effect mediated = 43.2%). Reductions in 70-week measures of fear avoidance, embarrassment avoidance, limiting activities, and all-or-nothing behavior all mediated improvement in fatigue at 70 weeks, although the causal direction of these cross-sectional effects cannot be determined. There were no between-group differences on measures of exercise capacity (a timed step test).

CONCLUSIONS: Improvements in fatigue following pragmatic rehabilitation are related to changes in behavioral responses to and beliefs about fatigue.

 

Source: Wearden AJ, Emsley R. Mediators of the effects on fatigue of pragmatic rehabilitation for chronic fatigue syndrome. J Consult Clin Psychol. 2013 Oct;81(5):831-8. doi: 10.1037/a0033561. Epub 2013 Jun 24. https://www.ncbi.nlm.nih.gov/pubmed/23796316

 

Cost-effectiveness of supported self-management for CFS/ME patients in primary care

Abstract:

BACKGROUND: Nurse led self-help treatments for people with chronic fatigue syndrome/myalgic encephalitis (CFS/ME) have been shown to be effective in reducing fatigue but their cost-effectiveness is unknown.

METHODS: Cost-effectiveness analysis conducted alongside a single blind randomised controlled trial comparing pragmatic rehabilitation (PR) and supportive listening (SL) delivered by primary care nurses, and treatment as usual (TAU) delivered by the general practitioner (GP) in North West England. A within trial analysis was conducted comparing the costs and quality adjusted life years (QALYs) measured within the time frame of the trial. 296 patients aged 18 and over with CFS/ME diagnosed using the Oxford criteria were included in the cost-effectiveness analysis.

RESULTS: Treatment as usual is less expensive and leads to better patient outcomes compared with Supportive Listening. Treatment as usual is also less expensive than Pragmatic Rehabilitation. PR was effective at reducing fatigue in the short term, but the impact of the intervention on QALYs was uncertain. However, based on the results of this trial, PR is unlikely to be cost-effective in this patient population.

CONCLUSIONS: This analysis does not support the introduction of SL. Any benefits generated by PR are unlikely to be of sufficient magnitude to warrant recommending PR for this patient group on cost-effectiveness grounds alone. However, dissatisfaction with current treatment options means simply continuing with ‘treatment as usual’ in primary care is unlikely to be acceptable to patients and practitioners.

TRIAL REGISTRATION: The trial registration number is IRCTN74156610.

 

Source: Richardson G, Epstein D, Chew-Graham C, Dowrick C, Bentall RP, Morriss RK, Peters S, Riste L, Lovell K, Dunn G, Wearden AJ; FINE Trial Writing group on behalf of the FINE Trial group. Collaborators (23). Cost-effectiveness of supported self-management for CFS/ME patients in primary care. BMC Fam Pract. 2013 Jan 18;14:12. doi: 10.1186/1471-2296-14-12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3556109/ (Full article)

 

Cognitions, behaviours and co-morbid psychiatric diagnoses in patients with chronic fatigue syndrome

Abstract:

BACKGROUND: Specific cognitions and behaviours are hypothesized to be important in maintaining chronic fatigue syndrome (CFS). Previous research has shown that a substantial proportion of CFS patients have co-morbid anxiety and/or depression. This study aims to measure the prevalence of specific cognitions and behaviours in patients with CFS and to determine their association with co-morbid anxiety or depression disorders.

METHOD: A total of 640 patients meeting Oxford criteria for CFS were recruited into a treatment trial (i.e. the PACE trial). Measures analysed were: the Cognitive Behavioural Response Questionnaire, the Chalder Fatigue Scale and the Work and Social Adjustment Scale. Anxiety and depression diagnoses were from the Structured Clinical Interview for DSM-IV. Multivariate analysis of variance was used to explore the associations between cognitive-behavioural factors in patients with and without co-morbid anxiety and/or depression.

RESULTS: Of the total sample, 54% had a diagnosis of CFS and no depression or anxiety disorder, 14% had CFS and one anxiety disorder, 14% had CFS and depressive disorder and 18% had CFS and both depression and anxiety disorders. Cognitive and behavioural factors were associated with co-morbid diagnoses; however, some of the mean differences between groups were small. Beliefs about damage and symptom focussing were more frequent in patients with anxiety disorders while embarrassment and behavioural avoidance were more common in patients with depressive disorder.

CONCLUSIONS: Cognitions and behaviours hypothesized to perpetuate CFS differed in patients with concomitant depression and anxiety. Cognitive behavioural treatments should be tailored appropriately.

 

Source: Cella M, White PD, Sharpe M, Chalder T. Cognitions, behaviours and co-morbid psychiatric diagnoses in patients with chronic fatigue syndrome. Psychol Med. 2013 Feb;43(2):375-80. doi: 10.1017/S0033291712000979. Epub 2012 May 9. https://www.ncbi.nlm.nih.gov/pubmed/22571806

 

Metacognitions and negative emotions as predictors of symptom severity in chronic fatigue syndrome

Abstract:

OBJECTIVE: Chronic fatigue syndrome (CFS) describes a condition that is primarily characterized by fatigue and flu-like symptoms that are not alleviated by rest. This study investigated the relationship among metacognitions, negative emotions, and symptom severity in CFS.

METHODS: A total of 96 patients who had received a diagnosis of CFS according to the Oxford Criteria completed a battery of self-report measures that consisted of the Depression Anxiety Stress Scales, the 30-Item Metacognitions Questionnaire, the Chalder Fatigue Questionnaire (CFQ), and the RAND 36-Item Short-Form Health Survey-Physical Functioning.

RESULTS: Correlation analyses showed that negative emotions and metacognitions were positively correlated with measures of symptom severity and that metacognitions were a better predictor of symptom severity than anxiety and depression. Hierarchical regression analyses indicated that (1) lack of cognitive confidence predicted both mental and physical factors of the CFQ and physical functioning independently of negative emotions and (2) beliefs about the need to control thoughts predicted the mental factor of the CFQ independently of negative emotions and lack of cognitive confidence.

CONCLUSION: The data support the potential application of the metacognitive model of psychological disorder to understanding CFS.

Copyright © 2011 Elsevier Inc. All rights reserved.

 

Source: Maher-Edwards L, Fernie BA, Murphy G, Wells A, Spada MM. Metacognitions and negative emotions as predictors of symptom severity in chronic fatigue syndrome. J Psychosom Res. 2011 Apr;70(4):311-7. doi: 10.1016/j.jpsychores.2010.09.016. Epub 2010 Nov 18. https://www.ncbi.nlm.nih.gov/pubmed/21414450

 

Comparison of adaptive pacing therapy, cognitive behaviour therapy, graded exercise therapy, and specialist medical care for chronic fatigue syndrome (PACE): a randomised trial

Abstract:

BACKGROUND: Trial findings show cognitive behaviour therapy (CBT) and graded exercise therapy (GET) can be effective treatments for chronic fatigue syndrome, but patients’ organisations have reported that these treatments can be harmful and favour pacing and specialist health care. We aimed to assess effectiveness and safety of all four treatments.

METHODS: In our parallel-group randomised trial, patients meeting Oxford criteria for chronic fatigue syndrome were recruited from six secondary-care clinics in the UK and randomly allocated by computer-generated sequence to receive specialist medical care (SMC) alone or with adaptive pacing therapy (APT), CBT, or GET. Primary outcomes were fatigue (measured by Chalder fatigue questionnaire score) and physical function (measured by short form-36 subscale score) up to 52 weeks after randomisation, and safety was assessed primarily by recording all serious adverse events, including serious adverse reactions to trial treatments. Primary outcomes were rated by participants, who were necessarily unmasked to treatment assignment; the statistician was masked to treatment assignment for the analysis of primary outcomes. We used longitudinal regression models to compare SMC alone with other treatments, APT with CBT, and APT with GET. The final analysis included all participants for whom we had data for primary outcomes. This trial is registered at http://isrctn.org, number ISRCTN54285094.

FINDINGS: We recruited 641 eligible patients, of whom 160 were assigned to the APT group, 161 to the CBT group, 160 to the GET group, and 160 to the SMC-alone group. Compared with SMC alone, mean fatigue scores at 52 weeks were 3·4 (95% CI 1·8 to 5·0) points lower for CBT (p = 0·0001) and 3·2 (1·7 to 4·8) points lower for GET (p = 0·0003), but did not differ for APT (0·7 [-0·9 to 2·3] points lower; p = 0·38). Compared with SMC alone, mean physical function scores were 7·1 (2·0 to 12·1) points higher for CBT (p = 0·0068) and 9·4 (4·4 to 14·4) points higher for GET (p = 0·0005), but did not differ for APT (3·4 [-1·6 to 8·4] points lower; p=0·18). Compared with APT, CBT and GET were associated with less fatigue (CBT p = 0·0027; GET p = 0·0059) and better physical function (CBT p=0·0002; GET p<0·0001). Subgroup analysis of 427 participants meeting international criteria for chronic fatigue syndrome and 329 participants meeting London criteria for myalgic encephalomyelitis yielded equivalent results. Serious adverse reactions were recorded in two (1%) of 159 participants in the APT group, three (2%) of 161 in the CBT group, two (1%) of 160 in the GET group, and two (1%) of 160 in the SMC-alone group.

INTERPRETATION: CBT and GET can safely be added to SMC to moderately improve outcomes for chronic fatigue syndrome, but APT is not an effective addition.

FUNDING: UK Medical Research Council, Department of Health for England, Scottish Chief Scientist Office, Department for Work and Pensions.

Copyright © 2011 Elsevier Ltd. All rights reserved.

Comment in:

 

Source: White PD, Goldsmith KA, Johnson AL, Potts L, Walwyn R, DeCesare JC, Baber HL, Burgess M, Clark LV, Cox DL, Bavinton J, Angus BJ, Murphy G, Murphy M, O’Dowd H, Wilks D, McCrone P, Chalder T, Sharpe M; PACE trial management group. Collaborators (19). Comparison of adaptive pacing therapy, cognitive behaviour therapy, graded exercise therapy, and specialist medical care for chronic fatigue syndrome (PACE): a randomised trial. Lancet. 2011 Mar 5;377(9768):823-36. doi: 10.1016/S0140-6736(11)60096-2. Epub 2011 Feb 18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065633/ (Full article)

 

Nurse led, home based self help treatment for patients in primary care with chronic fatigue syndrome: randomised controlled trial

Abstract:

OBJECTIVE: To evaluate the effectiveness of home delivered pragmatic rehabilitation-a programme of gradually increasing activity designed collaboratively by the patient and the therapist-and supportive listening-an approach based on non-directive counselling-for patients in primary care with chronic fatigue syndrome/myalgic encephalomyelitis or encephalitis (CFS/ME).

DESIGN: Single blind, randomised, controlled trial.

SETTING: 186 general practices across the north west of England between February 2005 and May 2007.

PARTICIPANTS: 296 patients aged 18 or over with CFS/ME (median illness duration seven years) diagnosed using the Oxford criteria.

INTERVENTIONS: Participants were randomly allocated to pragmatic rehabilitation, supportive listening, or general practitioner treatment as usual. Both therapies were delivered at home in 10 sessions over 18 weeks by one of three adult specialty general nurses who had received four months’ training, including supervised practice, in each of the interventions. GP treatment as usual was unconstrained except that patients were not to be referred for systematic psychological therapies during the treatment period. Main outcome measures The primary clinical outcomes were fatigue and physical functioning at the end of treatment (20 weeks) and 70 weeks from recruitment compared with GP treatment as usual. Lower fatigue scores and higher physical functioning scores denote better outcomes.

RESULTS: A total of 257 (87%) of the 296 patients who entered the trial were assessed at 70 weeks, the primary outcome point. Analysis was on an intention to treat basis, with robust treatment effects estimated after adjustment for missing data using probability weights. Immediately after treatment (at 20 weeks), patients allocated to pragmatic rehabilitation (n=95) had significantly improved fatigue (effect estimate -1.18, 95% confidence interval -2.18 to -0.18; P=0.021) but not physical functioning (-0.18, 95% CI -5.88 to +5.52; P=0.950) compared with patients allocated to treatment as usual (n=100). At one year after finishing treatment (70 weeks), there were no statistically significant differences in fatigue or physical functioning between patients allocated to pragmatic rehabilitation and those on treatment as usual (-1.00, 95% CI -2.10 to +0.11; P=0.076 and +2.57, 95% CI 3.90 to +9.03; P=0.435). At 20 weeks, patients allocated to supportive listening (n=101) had poorer physical functioning than those allocated to treatment as usual (-7.54, 95% CI -12.76 to -2.33; P=0.005) and no difference in fatigue. At 70 weeks, patients allocated to supportive listening did not differ significantly from those allocated to treatment as usual on either primary outcome.

CONCLUSIONS: For patients with CFS/ME in primary care, pragmatic rehabilitation delivered by trained nurse therapists improves fatigue in the short term compared with unconstrained GP treatment as usual, but the effect is small and not statistically significant at one year follow-up. Supportive listening delivered by trained nurse therapists is not an effective treatment for CFS/ME.

Trial registration International Standard Randomised Controlled Trial Number IRCTN74156610.

Comment in:

Pragmatic rehabilitation for chronic fatigue syndrome. [BMJ. 2010]

Nurse-delivered, home-based pragmatic rehabilitation has a short-term effect on improving fatigue in people with chronic fatigue syndrome compared with usual GP care, but effects were not sustained at 1 year. [Evid Based Nurs. 2010]

 

Source: Wearden AJ, Dowrick C, Chew-Graham C, Bentall RP, Morriss RK, Peters S, Riste L, Richardson G, Lovell K, Dunn G; Fatigue Intervention by Nurses Evaluation (FINE) trial writing group and the FINE trial group and 23 Collaborators. Nurse led, home based self help treatment for patients in primary care with chronic fatigue syndrome: randomised controlled trial. BMJ. 2010 Apr 23;340:c1777. doi: 10.1136/bmj.c1777. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2859122/ (Full article)