Department of Statistics, FIN-20014 University of Turku, Finland. virahola@utu.fi|Department of Statistics, FIN-20014 University of Turku, Finland. virahola@utu.fi|Department of Statistics, FIN-20014 University of Turku, Finland. virahola@utu.fi|Department of Statistics, FIN-20014 University of Turku, Finland. virahola@utu.fi