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Rapid Responses: Rapid Responses published:
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![[Read Rapid Response]](/icons/misc/sectionDOWN.gif)
IBS For The Long Run
- Jacobo Dib Jr MD (19 November 2008)
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The problem of insoluble fibre in irritable bowel syndrome
- Peter J Whorwell (2 December 2008)
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Homeopathy in treatment of Irritable Bowel Syndrome
- Elmuhtady M Said, Dr K Kapur,Mrs J Raw,Dr C M Smith. (15 December 2008)
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Treating irritable bowel syndrome: the old remedies are the best – so let’s not forget amitriptyline!
- John S Leeds, Clare M Leeds, David S Sanders (18 December 2008)
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Response to authors of previous rapid responses
- Alexander Ford, NIcholas J. Talley, Eamonn M. M. Quigley, Paul Moayyedi (15 January 2009)
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Error in figures 2, 3 and 4
- Mitchell Levine, Benjamin Asa (6 May 2009)
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A problem with logarithms
- Zekria Ibrahimi (12 May 2009)
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Another unhappy twist to this statistical saga
- Zekria Ibrahimi (13 May 2009)
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Forest plot: not seeing the wood for the logs
- Zekria Ibrahimi (15 May 2009)
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Re: Forest plot: not seeing the wood for the logs
- Douglas G Altman (18 May 2009)
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Re: Re: Forest plot: not seeing the wood for the logs
- Ibrahimi Zekria (18 May 2009)
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Mathematical problems are medical problems
- Zekria Ibrahimi (5 June 2009)
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Jacobo Dib Jr MD, Chief of the Gastroenterology Service Hospital de Lidice. Caracas, Venezuela.
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When dealing with IBS we have to think long term. In this study, the minimum duration of treatment of one week is not adequate. The argument given by the authors, that is, the time needed to achieve steady plasma concentrations is irrelevant, when at least one of the agents been evaluated is non absorbable material, that is, fibre. Fibre has to be taken for longer periods of time to expect a proper effect in IBS, unlike laxatives that can be ingested either chronically or on demand. Peppermint as well, when given in enteric-coated capsules, achieves its effect more locally in contact with the intestinal mucosa, than through systemic mechanisms. Nevertheless, this is an excellent paper that adds more evidence to old modalities of treatment, contributing to upgrade them to an upper level in the Evidence- Based Treatment scale. Competing interests: None declared |
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Peter J Whorwell, Professor of Medicine & Gastroenterology Wythenshawe Hospital, Manchester M23 9LT, UK
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I was surprised to read in the popular press that, according to the British Medical Journal, fibre is good for irritable bowel syndrome (IBS). In 1994 we raised the possibility that, at least in the secondary care setting, cereal fibre was actually more likely to do harm than good in patients with IBS(1). Today, as a gastroenterologist who probably sees more cases of severe IBS than the majority of my colleagues, I still find that the total exclusion of all cereal fibre, such as bran and brown bread, from the diet is one of the most rewarding treatment strategies I can offer these patients. In the body of their paper in the BMJ, Ford and colleagues(2) acknowledge that as opposed to ispaghula (soluble fibre), bran (insoluble fibre) is not effective in IBS but claim that the possibility of an exacerbation of symptoms by bran is not borne out by their findings, presumably because of the lack of side effects reported in the trials they reviewed. However, it has to be remembered that trials of fibre have traditionally looked for improvement or no improvement and do not even allow for the possibility of deterioration because fibre is considered a natural product that is 'harmless'. Indeed, for the same reason any worsening of symptoms is likely to be attributed more to a spontaneous exacerbation of the disorder rather than being regarded as a side effect of the bran. It seems reasonable to assume that the potentially harmful effects of bran are going to be exaggerated in secondary and tertiary care because, by definition, those individuals not made worse are less likely to be amongst those who are referred in the first place. We have confirmed this hypothesis by also studying the response to bran in primary care and demonstrating that bran is less deleterious in this setting, although it can still cause an exacerbation in some patients(3). We live in times characterised by evidence based medicine and the rapid dissemination of the results of research to the media. With respect to the former, we must still listen to what our patients are telling us especially when the question is subtly different to the question that has been addressed by the evidence. With regard to the latter, we must be extremely careful about the accuracy of what we write especially in the abstract of a paper as this is not infrequently the only part that is scanned by the busy reader. The concluding statement in the abstract of the paper by Ford et al is misleading as it completely ignores the substantial differences between soluble and insoluble fibre thus encouraging some IBS sufferers to continue with a treatment, insoluble fibre, which at best is doing them no good but at worst may be doing them harm. References 1. Francis CY, Whorwell PJ. Bran and irritable bowel syndrome: time for reappraisal. Lancet 1994;344:39-40. 2. Ford AC, Talley NJ, Spiegel BMR, Foxx-Orenstein AE, Schiller L, Quigley EMM, Moayyedi P. Effect of fibre, antispasmodics and peppermint oil in the treatment of irritable bowel syndrome: systematic review of the literature and meta-analysis. Btitish Medical Journal 2008;337;a2313. 3. Miller V, Lea R, Agrawal A, Whorwell PJ. Bran and irritable bowel syndrome: the primary-care perspective. Dig Liver Dis 2006;38:737-40. Competing interests: None declared |
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Elmuhtady M Said, Staff Grade in Gastroenterology Barnsley District General Hospital, Dr K Kapur,Mrs J Raw,Dr C M Smith.
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We read with great interrest the article by Alexander C Ford et al(1). It is estimated that 40% of all gastroenterology clinic visits are for Functional gastrointestinal disorders (2), which mainly include functional dyspepsia irritable bowel syndrome, and non-cardiac chest pain. They are difficult to treat because no single etiology for these disorders is known, and thus treatment is directed at controlling symptoms. A wide range of interventions is used in their management including Pharmacological and non-pharamacological approaches but there is difficulty in deciding upon a ‘treatment of choice’. Research studies on homeopathy as a non-pharmacological treatment have been contradictory in their findings. In Barnsley District General Hospital we are currently in the process of conducting a case series study to determine the optimum duration of adjunctive individualised homeopathic treatment for patients suffering from refractory gastroenterological conditions. Healthcare by a homeopath is best understood as a complex intervention consisting of a series of in depth interviews with a strong focus on the patient’s subjective experience, plus individually tailored homeopathic medicines. In a recent trial conducted in our trust, fibromyalgia syndrome (FMS) sufferers were randomised to usual care or usual care plus healthcare by a homeopath. Homeopathic treatment was found to be acceptable to patients and effective in the treatment of FMS. It will be interesting to see the outcome of this case series with regard to patients with irritable bowel syndrome and functional bowel problems. We are looking forward to publishing this study in the near future. References: 1-Alexander C Ford, Nicholas J Talley, Brennan M R Spiegel, Amy E Foxx- Orenstein, Lawrence Schiller, Eamonn M M Quigley, and Paul Moayyedi Effect of fibre, antispasmodics, and peppermint oil in the treatment of irritable bowel syndrome: systematic review and meta-analysis BMJ 2008; 337: a2313 2-Mitchell, CM; Drossman, DA. Survey of the AGA membership relating to patients with functional gastrointestinal disorders. Gastroenterology. 1987;92:1282–1284 Dr E Said, Staff Grade Doctor, Barnsley Hospital NHS Foundation Trust Dr K Kapur, Consultant Gastroenterologist, Barnsley Hospital NHS Foundation Trust Mrs J Raw, Registered Homeopath Dr C M Smith, Research Fellow Acute Care, Barnsley Hospital NHS Foundation Trust Competing interests: None declared |
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John S Leeds, Specialist Registrar in Gastroenterology Royal Hallamshire Hospital, Sheffield, S10 2JF, UK, Clare M Leeds, David S Sanders
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We read with interest the meta-analysis by Ford and colleagues (1). This important study provides a much needed supportive evidence base for our current practice. Jones also makes a critical point that a ‘holistic and integrated approach’ is necessary (2). With this perspective in mind we would like to make the suggestion that either within the ‘what is already known on this topic’ of Ford’s paper or in the discussion, that there should be the mention of the potential benefits of amitriptyline. At low dose (10mg – 25mg nocte) it appears that some patients particularly with diarrhoea predominant IBS derive symptomatic benefit. A recent meta- analysis by the same authors has suggested a positive effect with a number needed to treat of 4 (3). Although further work may be required in this area – amitriptyline still remains an ‘old’ but important addition to the clinicians’ armamentarium and is in keeping with a holistic approach when considering therapeutic options in IBS patients (4). 1. Ford AC, Talley NJ, Spiegel BMR, Foxx-Orenstein AE, Schiller L, Quigley EMM, Moayyedi P. Effect of fibre, antispasmodics and peppermint oil in the treatment of irritable bowel syndrome: systematic review of the literature and meta-analysis. BMJ 2008;337;a2313. 2. Jones R. Treatment of irritable bowel syndrome in primary care. BMJ 2008;337:a2213. 3. Ford AC, Talley NJ, Schoenfeld PS, Quigley EM, Moayyedi P. Efficacy of Antidepressants and Psychological Therapies in Irritable Bowel Syndrome: Systematic Review and Meta-analysis. Gut 2008. Nov 10 [Epub ahead of print]. 4. National Institute for Health and Clinical Excellence. Irritable bowel syndrome in adults. Diagnosis and management of irritable bowel syndrome in primary care. London: NICE, 2008. www.nice.org.uk/CG061. Competing interests: None declared |
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Alexander Ford, Lecturer in Medicine and Honorary SpR in Gastroenterology St. James's UNiversity Hospital Leeds, LS9 7TF, NIcholas J. Talley, Eamonn M. M. Quigley, Paul Moayyedi
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Editor We are grateful for the interest that our recent article concerning the efficacy of fibre, antispasmodic drugs, and peppermint oil in irritable bowel syndrome (IBS) has generated, and the important and exciting debate it has stimulated We agree with Dr. Dib that IBS is a chronic, relapsing and remitting condition. We chose a minimum duration of therapy in randomised controlled trials (RCTs) of the agents we studied in our systematic review and meta- analysis of 1 week for the reasons we discussed in our article. [1] However, 34 of the 35 eligible studies randomised patients to therapy in excess of 1 week. The remaining trial [2] did not have any significant impact on the overall conclusions when it was excluded from the analysis (number needed to treat (NNT) with antispasmodics = 6; 95% confidence interval 4 to 10). The minimum duration of therapy used in the trials of fibre in IBS that we identified was 4 weeks, and the majority of RCTs used 12 weeks or more. With regard to Professor Whorwell’s comments, we stated clearly in the abstract of our article that the beneficial effect of fibre was limited to ispaghula husk, [1] which is also known as psyllium. We cannot be held responsible for the misrepresentation of our findings by the “popular press”. Dr. Leeds et al. make the important point that antidepressant drugs, particularly tricyclic antidepressants, were also of benefit in IBS, with an NNT in our systematic review and meta-analysis of 4. [3] However, there was also a beneficial effect of a newer class of antidepressants, serotonin re-uptake inhibitors, in IBS in this meta-analysis. The NNT was 3.5, albeit in a smaller number of RCTs containing fewer patients. With respect to any role for non-pharmacological therapies in the management of IBS, we have also examined this issue. We are not aware of any published RCTs of homeopathy in IBS. There is an existing systematic review of the efficacy of various psychological therapies in IBS, conducted by Lackner et al., [4] which identified 10 trials that provided extractable dichotomous data for pooling. As Drs. Plotnikoff and Weisberg correctly state the NNT with psychological therapies reported in this systematic review was 2. While this may appear very appealing, unfortunately there were only a total of 185 patients included in these RCTs, and 9 of the 10 trials in this systematic review emanated from a single centre in the United States, which suggests that the treatment effect may have been overestimated. In our own systematic review and meta- analysis of the efficacy of psychological therapies in the management of IBS, which identified 20 RCTs containing 1278 patients, we reported an NNT to improve or cure 1 patient’s symptoms of 4. [3] We conducted a sensitivity analysis that excluded the 9 RCTs conducted by the same group of investigators, which demonstrated a reduced, though still statistically significant, treatment effect of psychological therapies on global IBS symptoms. There were only 2 of these 20 RCTs comparing hypnotherapy to supportive therapy or waiting list control in 40 patients. The medical management of IBS remains unsatisfactory, and no single intervention has been shown to alter the natural history of the condition convincingly, but data from these recent studies, which were performed to inform the updated American College of Gastroenterology monograph on the management of IBS, [5] suggest there are both pharmacological and psychological therapies that are effective in IBS, at least in the short- term. Authors Alexander C Ford1, Nicholas J Talley2, Eamonn MM Quigley3, Paul Moayyedi1. 1Gastroenterology Division, McMaster University, Health Sciences Centre, Hamilton, Ontario, L8N 3Z5, Canada. 2Professor of Medicine, Department of Medicine, Mayo Clinic Florida, Jacksonville, Florida, FL 32224, USA. 3Department of Medicine, Clinical Sciences Building, Cork University Hospital, Cork, Ireland. References 1. Ford AC, Talley NJ, Spiegel BMR, Foxx-Orenstein AE, Schiller L, Quigley EMM, Moayyedi P. Effect of fibre, antispasmodics, and peppermint oil in irritable bowel syndrome: Systematic review and meta-analysis. Br Med J 2008;337:a2313. 2. Virat J, Hueber D. Colopathy pain and dicetel. Prat Med 1987;43:32-34. 3. Ford AC, Talley NJ, Schoenfeld PS, Quigley EMM, Moayyedi P. Efficacy of antidepressants and psychological therapies in irritable bowel syndrome: Systematic review and meta-analysis [published online first: 10 November 2008]. Gut 2008;doi:10.1136/gut.2008.163162. 4. Lackner JM, Mesmer C, Morley S, Dowzer C, Hamilton S. Psychological treatments for irritable bowel syndrome: A systematic review and meta- analysis. J Consult Clin Psychol 2004;72:1100-13. 5. American College of Gastroenterology IBS Task Force. An evidence-based position statement on the management of irritable bowel syndrome. Am J Gastroenterol 2009;104 (suppl 1):S1-S35. Competing interests: Alexander C Ford: none declared. Nicholas J Talley: has received consultancy fees from Procter and Gamble, Lexicon Genetics, Inc., Astellas Pharma US, Inc., Pharma Frontiers, Ltd., Callisto Pharmaceuticals, AstraZeneca, Addex Pharma, Ferring Pharma, Salix, MGI Pharma, McNeil Consumer, Microbia, Dynogen, Conexus, Novartis, and Metabolic Pharmaceuticals, and has received research support from Novartis, Takeda, GlaxoSmithkline, Dynogen, and Tioga. Eamonn MM Quigley: has received consultant’s and speaker’s bureau fees from Nycomed, Boehringer Ingelheim, Procter and Gamble, Reckitt Benckiser and Prometheus, and holds equity in Alimentary Health. Paul Moayyedi: chair at McMaster University partly funded by an unrestricted donation by AstraZeneca, and has received consultant’s and speaker’s bureau fees from AstraZeneca, AxCan Pharma, Nycomed, and Johnson and Johnson. |
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Mitchell Levine, Professor McMaster University, Benjamin Asa
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We were reading this article only recently and noticed that there is a printing error in the labels for the x-axis in figures 2,3 and 4. The centre point should not be "zero", but should be labelled as "one". In addition, the numbers to the left of the centre point should not have negative values. When presenting relative risks in a figure it is not possible to plot zero anywhere on the axis, nor can a relative risk have a negative value. Since it is an on-line version that readers are accessing, I assume that changes to the document are still possible and you might want to consider correcting the problem. Competing interests: None declared |
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Zekria Ibrahimi, psychiatric patient Coombs Library UB1 3EU
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It is not pleasant to go where statisticians fear to tread. The article on how difficult it is to treat irritable bowel syndrome (1) ran into a quagmire of graphs (Figs 2, 3, 4). According to one rapid response (2), the x- axis wrongly implied there could be a negative relative risk. Relative risk is a ratio that can range from zero beyond 1 and then possibly to infinity. Infinity here would be merely theoretical, as so much unfortunately is in statistics. Relative risk compares control to treatment, non- exposed to exposed (3). So why were there negative values of relative risk on the graphs? What hellish error had been made? Ah, the spacings are not linear, but logarithmic. We have a logarithmic x- axis. And logarithms can be negative for fractions below one. The logarithm of one in base ten is- zero. So Figs 2, 3, and 4 would seem valid after all if they were in the form of logarithmic graphs. Still, they have proved confusing. They were not defined as logarithmic in the forest plots. And why choose logarithms? These would make the relative risk appear less than it actually was. Perhaps there was not enough space for an ordinary linear graph. Maybe the intention was to give the data an unfair graphical spin. And here is the twist in this statistical tale. By picking a log or a linear axis, we can make the data look as we would wish it to on a graph, for all sorts of malevolent purposes. We can squeeze it in or stretch it out. There are lies, damned lies, statistics- and graphs. REFERENCES: (1) Effects of fibre, antispasmodics, and peppermint oil in the treatment of irritable bowel syndrome: systematic review and meta- analysis. Alexander C Ford et al. BMJ 2008;337:a2313 (2) Error in figs 2,3, 4. BMJ Rapid Response. Mitchell Levine and benjamin Asa. 6 May. 2009. (3) Statistical Methods in Medical Research. P. Armitage, G.Berry, J.N.S.Matthews. Blackwell. Fourth edition. 2002. Psgs. 671- 673. Competing interests: None declared |
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Zekria Ibrahimi, psychiatric patient Coombs Library UB1 3Eu
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There is a general problem with these sort of forest plots for relative risk. Skimming uneasily through medical literature, one finds that relative risk is often formatted as in this article on irritable bowel syndrome (1) , viz with a logarithmic x- axis. Such representation verges on medically misleading, because of the contrary nature of logarithms. An increase of relative risk of, for example, one half, would occupy a small section on the side above one, but a much larger section on the side below one. Logarithms are not neat and linear. By definition, and most inconveniently here, they expand exponentially. So we have a medically skewed picture through such a logarithmic framework for relative risk. Fractional figures below one are stretched out; figures above one are (relatively) squeezed in. Presumably, logarithms are deployed because the data- always guaranteed to be irregular and nasty- would otherwise be scattered too far off the page. Alas, one might misuse such a logarithmic basis to almost misrepresent data on a graph. Relative risk above one would be rendered less important in terms of the graph, of the visual set- up. The transcription error partly happened because the logarithmic transformation of the data was not being made explicit. Yet again, the mathematics and the medicine are capable of being at cross purposes. These two monsters just do not want to trot prettily in tandem. REFERENCES: (1) Effect of fibre, antispasmodics and peppermint oil in the treatment of irritable bowel syndrome: systematic review and meta- analysis. Alexander C Ford et al. BMJ 2008; 337: a2313 Competing interests: None declared |
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Zekria Ibrahimi, psychiatric patient Coombs Library UB1 3EU
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According to Wikipedia (1), a forest plot may have a natural logarithmic scale on the x- axis so that confidence intervals can appear symmetrical about the means, and ratios (relative risk being a ratio) seem equivalent both above one and below one. A log scale will give the same length in a confidence interval for a ratio of ten, whether this is ten to one or one to one tenth. 'One' at the bottom of the y- axis is the null hypothesis of no effect. The forest plot provides a display of the null hypothesis as the y - axis. If the confidence interval intrudes on this y- axis, then there is no statistical significance. But ... the forest plot on a logarithmic scale still may be capable of the lie factor (2)- that is, graphical misrepresentation. How? Natural logaritms are to base e, that is, 2.718 ... Confidence intervals are worked out to base e in the BMJ book, Statistics with Confidence (3). However, most forest plots are to base 10, not base e. Traipsing unsteadily through the Internet, I also happened upon a forest plot of base 2 on the x- axis(4). There are linear forest plots too. Different log bases would manipulate the visual lay- out, perhaps to misrepresent data. I am not a mathematician, and my own previous rapid responses to this article, and indeed the transcription error in the article, indicate the confusion possible over forest plots and their x- axis. The difficulty with the x- axis in forest plots emerges most when the effect size is numbers needed to treat- then the null hypothesis is set at infinity (5)! The term, forest plot, only emerged during the 1990's. The unhappy suggestion has to be that it remains an immature statistical device. It is not yet thoroughly confident and sound in root and branch. As far as forest plots are concerned, one is not seeing the wood for the logs! REFERENCES: (1) Forest Plot. Wikipedia. (2) The Cambridge Dictionary of Statistics in the Medical Sciences. B. S. Everitt. CUP. 1995. Pg. 142. (3) Statistics with Confidence- Confidence intervals and statistical guidelines. Martin J Gardner and Douglas G Altman. BMJ. 1990. Pgs. 51-52. (4) Statins and cancer Risk: A Literature- Based Meta- Analysis and Meta- Regression Analysis of 35 Randomized Controlled trials. Journal of Clinical Oncology. Vol. 24. No. 30. Pgs. 4808-4817. (October 20). 2006. S. Bonovas et al. (5) Confidence intervals for the number needed to treat. Douglas G Altman. BMJ 1998;317:1309-12. Competing interests: None declared |
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Douglas G Altman, Professor of Statistics in Medicine Centre for Statistics in Medicine, University of Oxford, Wolfson College, Linton Rd, Oxford OX2 6UD
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It would be unfortunate if Zekria Ibrahimi’s comments (1) mislead anyone into thinking that forest plots are unreliable. It is of course true that logarithms to base 10 or base 2 give different values. But when a confidence interval is calculated for a quantity on a log scale (such as log relative risk) the values obtained are then back- transformed to the original scale (here, the relative risk). Thus the answer will be the same whether using logs to base 2, 10, e or anything else. So the forest plot for a meta-analysis will look identical regardless of the base used as long as the scale shows the relative risk, not the log relative risk, as is good practice. It is not correct to say that "different log bases would manipulate the visual lay-out, perhaps to misrepresent data." In the paper by Ford et al (2) the relative risk was indeed plotted on a log scale rather than the log relative risk being plotted. Unfortunately the original axis labelling incorrectly showed some negative values, but a correction was posted on 8 May. The comment about number needed to treat (NNT) is also misleading as the NNT should never be used as the basis for a meta-analysis. Douglas G Altman 1 Ibrahimi Z. Forest plot: not seeing the wood for the logs. http://www.bmj.com/cgi/eletters/337/nov13_2/a2313#213704 2 Ford AC, Talley NJ, Spiegel BMR, Foxx-Orenstein AE, Schiller L, Quigley EMM, Moayyedi P. Effect of fibre, antispasmodics, and peppermint oil in irritable bowel syndrome: Systematic review and meta-analysis. BMJ 2008;337:a2313. Competing interests: None declared |
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Ibrahimi Zekria, psychiatric patient Coombs Library
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I thank Professor Altman for his response, since science cannot progress without scepticism- or debate. The lie factor is not Einstein with graphs! Take, for example, a meta - analysis where the relative risks are all between 1 and 2. Then a spaced out x- axis to log base two will make the figures seem move removed from the y- axis than an x- axis to log base ten. Of course, the real data are the same, but the appearances? Ha! It is just a mere visual thing, it is not high powered mathematics (1). Some relative risks in forest plots are on a linear axis, and then we would have all sorts of distortions to the confidence intervals. The mathematical problem is that the standard error, and therefore the confidence interval, with relative risk (as a ratio) is logarithmic (base e). Statistical theory would be impossible without that natural log, e. As for numbers needed to treat, this seems a practical down to earth sort of way for clinicians to examine data. That a meta- analysis, according to Professor Altman, is unable to include numbers needed to treat is a sign something is deficient about the excessively theoretical nature of a meta- analysis. What of absolute risk difference? Again, the way this looks visually would alter according to what sort of x- axis lay out we had. The damned lies label on statistics derives from spinning identical data, often through graphs, to make it look different- quite unjustifiably. REFERENCES: The Cambridge Dictionary of Statistics in the Medical sciences. B. S. Everitt. 1995. Pg. 142. 'Lie factor=apparent size of effect show in graph divided by actual size of effect in data' Competing interests: None declared |
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Zekria Ibrahimi, psychiatric patient Coombs Library UB1 3EU
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This is a late apology to Professor Altman about how I was so misleading in my trek through log scales and meta-analyses. I have been confused and confusing. Customarily, a forest plot will have a relative risk (or odds ratio) on a logarithmic x- axis. A log axis is resorted to because the standard error of relative risk is logarithmic (1). A linear framework would possess skewed, irregular confidence intervals, which are based on the standard errors. One is unhappily reminded of Alice's uncomfortable variations in dimensions through that vertiginous looking glass. With numbers needed to treat, another difficulty pops up- that the null hypothesis of no effect is at infinity. Various weird things then happen to the confidence intervals! (2) A forest plot becomes most problematic. Curiouser and curiouser... What one might fear is that forest plots are not always 'particularly elegant and intuitively comprehensible' (3). They suffer from mathematical complexities, revolving round the confidence intervals. There are relative axes that are linear, that are to log 2 or log 10, that could thus be manipulated to make them appear what they are not in the cliche of evidence biased medicine. Professor Altman claims: 'the NNT should never be used as the basis for a meta- analysis' (4). But the actual article on Irritable Bowel Syndrome (IBS) is a meta- analysis that does resort to numbers needed to treat (5). NNT is quoted in the conclusion ('What This Study Adds'). NNT is a mathematical draw- back only when the confidence interval is not statistically significant. NNT is, as Professor Altman nervously implies, only partially applicable in a meta- analysis. Anti- spasmodics are said to be first- line treatment by NICE and the British Society of Gastroenterology, but have an inferior NNT to the apparently natural remedy of peppermint oil. Peppermint oil is not recommended at all in the official prescribing guidelines. Without this article, and its homely reliance on NNT, we would be less aware of the peppermint oil factor in IBS. Graphs more than any other part of statistical presentation can be prone to deformation and distortion. Against all the brave efforts of people such as Professor Altman, not enough down to earth explanations of statistical methods exist. Medicine is even more bewildered than Alice as it confronts the Chesire cats and Jabberwockys of mathematics. Mathematical problems can be medical problems. Again I am sorry to Professor Altman and the BMJ for having been such an idiot over these dreadfully complex issues. Any layman must feel bewildered by the not always well fitting nexus between medicine and mathematics. REFERENCES: (1) Statistics with Confidence. M.J.Gardner and D.G.Altman. BMJ. 1990. pg.52. (2) Confidence Intervals and the number needed to treat. D.G.Altman. BMJ 1998;317:1309-12/ (3) How to read and understand and use systematic reviews and meta- analyses. S.Leucht et al. Acta Psychiatr Scand 2009:119:pg. 447. (4) Re: Forest Plot: not seeing the wood for the logs. BMJ Rapid response. D.G.Altman. 18 May 2009. (5) Effect of fibre, antispasmodics and peppermint oil in the treatment of irritable bowel syndrome: systematic review and meta- analysis. Alexander c. Ford et al. BMJ 2008;337:a2313. Competing interests: None declared |
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