“…There are different techniques and proposals based on: (1) cross-efficiency DEA models (Sexton et al 1986, Doyle, Green 1994, Adler et al 2002; (2) super-efficiency models (Andersen, Petersen 1993, Zhu 1996, Seiford, Zhu 1998; and (3) virtual efficiency models (Bazargan, Vasigh 2003, Martín, Román 2006, Barzegarinegad et al 2014, Martín et al 2017). …”