1. Department of Mathematics and Mathematical Statistics; Umeå University; Umeå Sweden
2. Department of Community Medicine and Rehabilitation; Umeå University; Umeå Sweden
3. Department of Statistics, Umeå School of Business, Economics and Statistics; Umeå University; Umeå Sweden
4. Department of Statistical Sciences; Università Cattolica del Sacro Cuore; Milan Italy
5. MOX - Modelling and Scientific Computing Laboratory, Department of Mathematics; Politecnico di Milano; Milan Italy