The effectiveness of parent training as a treatment for preschool attention-deficit/hyperactivity disorder: study protocol for a randomized controlled, multicenter trial of the New Forest Parenting Program in Everyday Clinical Practice - Lange, A M; Daley, D; Frydenberg, M; Rask, C U; Sonuga-Barke, E; Thomsen, P H (JMIR Res Protoc, 2016)