Powell, Jane E., Bird, Emma L., Jago, Russell, Edwards, Mark J., Sebire, Simon J., Powell, Jane, Cooper, Ashley R., Bird, Emma, Simon, Joanne, Blair, Peter S., "Bristol girls dance project (BGDP): protocol for a cluster randomised controlled trial of an after-school dance programme to increase physical activity among 11-12 year old girls", BMC public health, 2013