Sixteen studies were include in the meta-analysis.The main characteristics are summarised in online Table DS1.Fourteen studies focused exclusively on somatoform disorder; two studies include patient with a range of mental disorder but were eligible because statistics for the somatoform disorder subgroup were reported separately. All studies but one were published after 2000. Ten studies were conducted in Germany, two in the USA,two in the Netherland, one in turkey,and one in China.