This new systematic review by proponents of homeopathy (and supported by a grant from the Manchester Homeopathic Clinic) tested the null hypothesis that “the main outcome of treatment using a non-individualised (standardised) homeopathic medicine is indistinguishable from that of placebo“. An additional aim was to quantify any condition-specific effects of non-individualised homeopathic treatment. In reporting this paper, I will stay very close to the published text hoping that this avoids both misunderstandings and accusations of bias on my side:
Literature search strategy, data extraction and statistical analysis followed the methods described in a pre-published protocol. A trial comprised ‘reliable evidence’ if its risk of bias was low or it was unclear in one specified domain of assessment. ‘Effect size’ was reported as standardised mean difference (SMD), with arithmetic transformation for dichotomous data carried out as required; a negative SMD indicated an effect favouring homeopathy.
The authors excluded the following types of trials: studies of crossover design; of radionically prepared homeopathic medicines; of homeopathic prophylaxis; of homeopathy combined with other (complementary or conventional) intervention; for other specified reasons. The final explicit exclusion criterion was that there was obviously no blinding of participants and practitioners to the assigned intervention.
Forty-eight different clinical conditions were represented in 75 eligible RCTs; 49 were classed as ‘high risk of bias’ and 23 as ‘uncertain risk of bias’; the remaining three trials displayed sufficiently low risk of bias to be designated reliable evidence. Fifty-four trials had extractable data: pooled SMD was -0.33 (95% confidence interval (CI) -0.44, -0.21), which was attenuated to -0.16 (95% CI -0.31, -0.02) after adjustment for publication bias. The three trials with reliable evidence yielded a non-significant pooled SMD: -0.18 (95% CI -0.46, 0.09). There was no single clinical condition for which meta-analysis produced reliable evidence.
A meta-regression was performed to test specifically for within-group differences for each sub-group. The results showed that there were no significant differences between studies that were and were not:
- included in previous meta-analyses (p = 0.447);
- pilot studies (p = 0.316);
- greater than the median sample (p = 0.298);
- potency ≥ 12C (p = 0.221);
- imputed for meta-analysis (p = 0.384);
- free from vested interest (p = 0.391);
- acute/chronic (p = 0.796);
- different types of homeopathy (p = 0.217).
After removal of ‘C’-rated trials, the pooled SMD still favoured homeopathy for all sub-groups, but was statistically non-significant for 10 of the 18 (included in previous meta-analysis; pilot study; sample size > median; potency ≥12C; data imputed; free of vested interest; not free of vested interest; combination medicine; single medicine; chronic condition). There remained no significant differences between sub-groups—with the exception of the analysis for sample size > median (p = 0.028).
Meta-analyses were possible for eight clinical conditions, each analysis comprising two to 5 trials. A statistically significant pooled SMD, favouring homeopathy, was observed for influenza (N = 2), irritable bowel syndrome (N = 2), and seasonal allergic rhinitis (N = 5). Each of the other five clinical conditions (allergic asthma, arsenic toxicity, infertility due to amenorrhoea, muscle soreness, post-operative pain) showed non-significant findings. Removal of ‘C’-rated trials negated the statistically significant effect for seasonal allergic rhinitis and left the non-significant effect for post-operative pain unchanged; no higher-rated trials were available for additional analysis of arsenic toxicity, infertility due to amenorrhoea or irritable bowel syndrome. There were no ‘C’-rated trials to remove for allergic asthma, influenza, or muscle soreness. Thus, influenza was the only clinical condition for which higher-rated trials indicated a statistically significant effect; neither of its contributing trials, however, comprised reliable evidence.
The authors concluded that the quality of the body of evidence is low. A meta-analysis of all extractable data leads to rejection of our null hypothesis, but analysis of a small sub-group of reliable evidence does not support that rejection. Reliable evidence is lacking in condition-specific meta-analyses, precluding relevant conclusions. Better designed and more rigorous RCTs are needed in order to develop an evidence base that can decisively provide reliable effect estimates of non-individualised homeopathic treatment.
I am sure that this paper will lead to lively discussions in the comments section of this blog. I will therefore restrict my comments to a bare minimum.
In my view, this new meta-analysis essentially yield a negative result and confirms most previous, similar reviews.
- It confirms Linde’s conclusion that “insufficient evidence from these studies that homeopathy is clearly efficacious for any single clinical condition”.
- It confirms Linde’s conclusion that “there was clear evidence that studies with better methodological quality tended to yield less positive results”.
- It confirms Kleinjen’s conclusion that “most trials are of low methodological quality”.
- It also confirms the results of the meta-analysis by Shang et al (much-maligned by homeopaths) than “finding is compatible with the notion that the clinical effects of homoeopathy are placebo effects.”
- Finally, it confirms the conclusion of the analysis of the Australian National Health and Medical Research Council: “Homeopathy should not be used to treat health conditions that are chronic, serious, or could become serious. People who choose homeopathy may put their health at risk if they reject or delay treatments for which there is good evidence for safety and effectiveness. People who are considering whether to use homeopathy should first get advice from a registered health practitioner. Those who use homeopathy should tell their health practitioner and should keep taking any prescribed treatments.”
Another not entirely unimportant point that often gets missed in these discussions is this: even if we believe (which I do not) the most optimistic interpretation of these (and similar data) by homeopaths, we ought to point out that there is no evidence whatsoever that homeopathy cures anything. At the very best it provides marginal symptomatic relief. Yet, the claim of homeopaths that we hear constantly is that homeopathy is a causal and curative therapy.
The first author of the new meta-analysis is an employee of the Homeopathy Research Institute. We might therefore forgive him that he he repeatedly insists on dwelling on largely irrelevant (i. e. based on unreliable primary studies) findings. It seems obvious that firm conclusions can only be based on reliable data. I therefore disregard those analyses and conclusions that include such studies.
In the discussion, the authors of the new meta-analysis confirm my interpretation this by stating that they “reject the null hypothesis (non-individualised homeopathy is indistinguishable from placebo) on the basis of pooling all studies, but fail to reject the null hypothesis on the basis of the reliable evidence only.” And, in the long version of their conclusions, we find this remarkable statement: “Our meta-analysis of the current reliable evidence base therefore fails to reject the null hypothesis that the outcome of treatment using a non-individualised homeopathic medicine is not distinguishable from that using placebo.” A most torturous way of stating the obvious: the more reliable data show no difference between homeopathy and placebo.