including poor randomization. A separate 2001 systematic review that assessed the quality of clinical trials of homeopathy found that such trials were generally of lower quality than trials of conventional medicine. A related issue is publication bias: researchers are more likely to submit trials that report a positive finding for publication, and journals prefer to publish positive results. Publication bias has been particularly marked in alternative medicine journals, where few of the published articles (just 5% during the year 2000) tend to report null results. Regarding the way in which homeopathy is represented in the medical literature, a systematic review found signs of bias in the publications of clinical trials (towards negative representation in mainstream medical journals, and vice versa in alternative medicine journals), but not in reviews. Positive results are much more likely to be false if the prior probability of the claim under test is low. Systematic reviews and meta-analyses of efficacy Both meta-analyses, which statistically combine the results of several randomized controlled trials, and other systematic reviews of the literature are essential tools to summarize evidence of therapeutic efficacy. Early systematic reviews and meta-analyses of trials evaluating the efficacy of homeopathic preparations in comparison with placebo more often tended to generate positive results, but appeared unconvincing overall. In particular, reports of three large meta-analyses warned readers that firm conclusions could not be reached, largely due to methodological flaws in the primary studies and the difficulty in controlling for publication bias. The positive finding of one of the most prominent of the early meta-analyses, published in The Lancet in 1997 by Linde et al., was later reframed by the same research team, who wrote: The evidence of bias [in the primary studies] weakens the findings of our original meta-analysis. Since we completed our literature search in 1995, a considerable number of new homeopathy trials have been published. The fact that a number of the new high-quality trials ... have negative results, and a recent update of our review for the most "original" subtype of homeopathy (classical or individualized homeopathy), seem to confirm the finding that more rigorous trials have less-promising results. It seems, therefore, likely that our meta-analysis at least overestimated the effects of homeopathic treatments. Subsequent work by John Ioannidis and others has shown that for treatments with no prior plausibility, the chances of a positive result being a false positive are much higher, and that any