Economies of scope in two-stage production systems: A data envelopment analysis approach Leila Zeinalzadeh Ahranjani, Reza Kazemi Matin and Reza Farzipoor Saen RAIRO-Oper. Res., 52 2 (2018) 335-349 Published online: 31 May 2018 DOI: 10.1051/ro/2017023