Erratum to: Singing classes for chronic obstructive pulmonary disease: a randomized controlled trial

In our 2012 paper on the effect of singing classes for patients with COPD which compared them to participation in a films studies group, we cited the wrong clinical trial number - (ISRCTN17544114). This number in fact relates to a previous study we had undertaken, published in 2010 which also evaluated singing classes in COPD but had compared them to a "usual care" arm.