†Statistical methods described in materials and methods section of paper.‡Standard error of the mean, confidence interval, standard deviation or other error measurement.*70% (174/247); 91% (247/271) of all included studies used statistical methods to analyse the data; 17% (46/267) of the studies, that presented numerical data, did not present a measure of variation (e.g. standard deviation) or uncertainty (e.g. standard error of the mean [SEM] or confidence interval [CI]).