Due to an error at the correction stage the fourth author's name was incorrectly listed. It should have appeared as: J. A. Engh
The correct version of the full author group is given below:
P. A. Ringen, T. V. Lagerberg, A. B. Birkenæs, J. A. Engh, A. Færden, H. Jónsdottir, R. Nesvåg, S. Friis, S. Opjordsmoen, F. Larsen, I. Melle and O. A. Andreassen