To the Editors:

The comments by Schieir and colleagues complicates an issue that is self evident: a pooled effect incorporates the bias from the individual trials. In our review we clearly acknowledged that the individual trials provide potentially biased estimates of treatment effects. For example, the first sentence of our conclusion was, “The available data on the effect of Tai Chi are sparse and derived principally from low-quality studies.” That is why we are now conducting our own trial to provide a more definitive answer (1).

We disagree with the authors' suggestion of avoiding meta-analysis as a solution to potential bias in trials. Avoiding meta-analysis does not solve the underlying problem because meta-analysis did not introduce the bias; it arose in the conduct and reporting of trials. There are methods to assess the likely extent of publication bias in a meta-analysis (e.g., funnel plot), but they require a reasonable number of trials and variation in sample size. Unfortunately, with only 7 trials these methods were not relevant in this review. We did however provide readers with information on the methodologic quality of each trial using a validated scale (2–4).


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  • 1
    Hall A, Maher CG, Latimer J, Ferreira M, Lam P. A randomized controlled trial of Tai Chi for long-term low back pain (TAI CHI): study rationale, design, and methods. BMC Musculoskelet Disord 2009; 10: 55.
  • 2
    Maher C, Sherrington C, Herbert R, Moseley A, Elkins M. Reliability of the PEDro sale for rating quality of randomized controlled trials. Phys Ther 2003; 83: 71321.
  • 3
    De Morton N. The PEDro scale is a valid measure of the methodological quality of clinical trials: a demographic study. Aust J Physiother 2009; 55: 12933.
  • 4
    Bhogal SK, Teasell RW, Foley NC, Speechley MR. The PEDro scale provides a more comprehensive measure of methodological quality than the Jadad scale in stroke rehabilitation literature. J Clin Epidemiol 2005; 58: 66873.

Amanda Hall MPE, BKIN*, Chris Maher PhD*, Jane Latimer PhD*, Manuela Ferreira PhD†, * The George Institute for International Health, The University of Sydney, Sydney, New South Wales, Australia, † The University of Sydney Sydney, New South Wales, Australia.