<p>The diamond represents a pooled effect estimate. Paired analyses were applied to all crossover trial <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107391#pone.0107391-Elbourne1" target="_blank">[18]</a>. Data are mean differences (MD) with 95% CI. <i>P</i> values are for Generic Inverse Variance random effects models. Inter-study heterogeneity was tested by the Cochran Q statistic at a significance level of <i>P</i> <0.10 and quantified by the I<sup>2</sup> statistic, where I<sup>2</sup> ≥ 50% is considered to be evidence of substantial heterogeneity.</p
