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Wrong test of heterogeneity used?
- Marjolein Y Berger (23 October 1998)
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PLEASE, no more relative risks/odds ratios/risk ratios!
- Yogi Sehgal (12 November 1998)
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Antibiotics for acute sinusitis in general practice
- G G Browning (27 November 1998)
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Marjolein Y Berger
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de Ferranti et al 1 conclude that because of a lack of statistical heterogeneity a pooled risk ratio of clinical failure is the best estimate of the effectiveness of antibiotics in acute sinusitis. In fact the statistical test they used to evaluate the hypothesis of homogeneity, with a P<0.1 to indicate significance, has a very low power to reveal statistical heterogeneity2. As many authors stated before, testing for (a high degree of) statistical heterogeneity is a necessary criterion, but is not sufficient for assessing the clinical importance of differences in inclusion criteria and methodology3. The six included placebo controlled, randomized trials showed important clinical heterogeneity. In particular heterogeneity concerning the setting of the studies, the extent of the disease in the included patients, the diagnosis of sinusitis, and the duration of therapy. These differences incorporate more than only a difference in the prior chance (or prevalence) of acute sinusitis. Severity and extent of the sinusitis may affect the ability of antibiotics to improve the symptoms. Duration of therapy may affect the ability of antibiotics: "to improve symptoms within 48 hours after the end of therapy". The pooled estimate of the risk ratio for clinical failure therefore tries to create apple-oranges5. In our opinion the conclusion of this analysis should be that evidence of the effectiveness of antibiotics in acute sinusitis is sparse and even rather doubtful in the setting were sinusitis is defined by clinical criteria alone, that is in the setting of the general practitioner. Marjolein Y Berger General practitioner, Research fellow Roos Bernsen Research fellow Department of General Practice, Room Fe315 Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam The Netherlands. 1 De Ferranti SD, Ioannidis PA, Lau J, Anninger V, Barza M. Are amoxycillin and folate inhibitors as effective as other antibiotics for acute sinusitis? A meta-analysis.BMJ, 1998;317:632-36. 2 Van Houwelingen HC. Meta-analysis; methods, limitations and applications. Biocybernetics Biomed Eng 1995;15:53-61. 3 Naylor CD. Meta-analysis and the meta-epidemiology of clinical research. BMJ 1997;315:617-19. 4 Greenhalgh T, Commentary: Meta-analysis is a blunt and potentially misleading instrument for analysing models of service delivery. BMJ 1998;317:390. |
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Yogi Sehgal, family physician terrace bay, ontario, canada
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In the interest of applying science to practical medicine, could we all PLEASE stop using relative risk/odds ratios to present data. I would love to see the absolute risks, absolute risk reductions and numbers needed to treat for antibiotics versus placebo in acute sinusitis in your data set. Also, the lack of defined inclusion criteria for patients, whether there is heterogeneity or not, does severely limit the applicability of the results to clinical practice. It would also be interesting to see side effects in antibiotics versus placebo (i.e. for any patients that got better with antibiotics, how many felt worse?), and were there any differences in more serious complications (meningitis, periorbital cellulitis), if in fact they are related... YS |
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G G Browning
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The paper "Meta-analysis on antibiotics in acute sinusitis?" in a section headed 'General Practice'1 could be criticised in many ways. This paper is presumably aimed at general practitioners in the United Kingdom to guide them in their use or non-use of antibiotics in patients with acute sinusitus. The authors rightly try and answer this by first looking at the RCT's on the effectiveness of antibiotics against non-antibiotic management and carried out a meta-analysis in the six placebo controlled trials they identified. By doing so it is implied that the patients being randomised were similar in each of the six studies to allow a meta- analysis to be performed. This is not the case. One of the papers (Wald et al, 1986) treated children, and cannot be combined with the other five papers that are adult studies. Table 1 shows the clinical settings and the entry criterion for the other five studies. In looking at this, a reader has to identify which study is applicable to their own clinical setting. The first study required a positive diagnostic irrigation, the second a positive bacteriological culture, the third a positive CT scan, and the fourth a positive straight X-ray for a patient to be included. The entry criterion in these four studies are thus grossly different and invalidate them being combined. The fifth study was the only one that had clearly defined symptomatic entry criteria that a reader could apply to their own practice and did not rely on investigation, which is likely to be the case in the majority of British primary care centres. The title of this paper2 embodies the most usual situation that general practitioners face 'adults with acute sinusitus-like complaints'. This study showed no effect of antibiotic (deoxycycline) versus placebo on the mean day of resolution of facial pain, and resumption of daily activities in 192 randomised patients. Though a power analysis is not reported to have been performed to exclude a type I error, the number of patients in this study is sufficiently large to exclude a clinically material difference. Hence this RCT should be the main evidence on which most general practitioners should base their practice until other studies in similar situations show otherwise - that antibiotics have no effect in 'adults with acute sinusitus-like complaints'. A meta-analysis of which antibiotic is best in acute sinusitus is thus made redundant and the rest of the paper irrelevant. Browning GG, Professor of Otolaryngology and Hear & Neck Surgery, University of Glasgow, Royal Infirmary, Glasgow G31 2ER 1. de Ferranti SD, Ioannidis JPA, Lau J, Anninger WV, Barza M. Are amoxycillin and folate inhibitors as effective as other antibiotics for acute sinusitis? A meta-analysis. BMJ 1998;317:632-7 2. Stalman W, van Essen GA, van der Graaf Y, de Melker RA. The end of antibiotic treatment in adults with acute sinusitis-like complaints in general practice? A placebo-controlled double-blind randomixed doxycycline trial. Br J Gen Pract 1997;47:794-9 Table |
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