Computing variance for interval data is NP-hard. - Scott Ferson; Lev Ginzburg; Vladik Kreinovich; Luc Longpré; Monica Aviles (SIGACT News, 2002)

Exact Bounds on Finite Populations of Interval Data. - Scott Ferson; Lev Ginzburg; Vladik Kreinovich; Luc Longpré; Monica Aviles (Reliab. Comput., 2005)