International comparison of trial results

Nearly two decades ago colleagues from the Cochrane Complementary and Alternative Medicine (CAM) Field found that a high proportion of trials originating from Eastern Asia or Eastern Europe tended to report positive results – nearly 100% in some cases.[1] This was not only for acupuncture trials but also for trials in other topics. More recently, a team led by Professor John Ioannidis, a renowned epidemiologist, conducted a meta-epidemiological study (a methodological study that examines and analyses data obtained from many systematic reviews/meta-analyses) and showed that treatment effects reported in trials conducted in less developed countries are generally larger compared with those reported in trials undertaken in more developed countries.[2] Many factors could have contributed to these observations, for example, publication bias, reporting bias, rigour of scientific conduct, difference in patient populations and disease characteristics, and genuine difference in intervention efficacy. While it is almost certain that the observation was not attributed to genuine difference in intervention efficacy alone, teasing out the influence of various factors is not an easy task. Lately, colleagues from CLAHRC WM have compared results from cardiovascular trials conducted in Europe with those conducted in North America, and did not find a convincing difference between them.[3] Perhaps the more interesting findings will come from the comparison between trials from Europe/America and those from Asia. The results? The paper is currently in press, so watch this space!

— Yen-Fu Chen, Senior Research Fellow


  1. Vickers A, Goyal N, Harland R, Rees R. Do certain countries produce only positive results? A systematic review of controlled trials. Controlled Clin Trials. 1998; 19(2): 159-66.
  2. Panagiotou OA, Contopoulos-Ioannidis DG, Ioannidis, JPA, Rehnborg CF. Comparative effect sizes in randomised trials from less developed and more developed countries: meta-epidemiological assessment. BMJ. 2013; 346: f707.
  3. Bowater RJ, Hartley LC, Lilford RJ. Are cardiovascular trial results systematically different between North America and Europe? A study based on intra-meta-analysis comparisons. Arch Cardiovasc Dis. 2015; 108(1):23-38.

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