The parenthood penalty in mental health : evidence from Austria and Denmark / Alexander Ahammer (Johannes Kepler University Linz and IZA), Ulrich Glogowsky (Johannes Kepler University Linz and CESifo), Martin Halla (Johannes Kepler University Linz, IZA and GÖG), Timo Hener (Aarhus University and CESifo) ; IZA Institute of Labor Economics