Barbi, Elisabetta, and Carlo G. Camarda. “Period and Cohort Effects on Elderly Mortality: A New Relational Model for Smoothing Mortality Surfaces”. Statistica 71, no. 1 (January 1, 2011): 51–69. Accessed May 17, 2022. https://rivista-statistica.unibo.it/article/view/3604.