Ali Abbasi Molai - School of Mathematics and Computer Science, Damghan University, Damghan, P.O.Box ۳۶۷۱۵-۳۶۴, Iran
Seyyed Hashem Mousavipour - School of Mathematics and Computer Science, Damghan University, Damghan, P.O.Box ۳۶۷۱۵-۳۶۴, Iran

Parallel production system consists of a number of divisions which operate independently within the system. When all data have crisp values, according to previous researches, the system efficiency is measured from a relational data envelopment analysis model. The system efficiency is a weighted average of the division efficiencies. The aim of this paper is to present a pair of two-level programming models to compute the lower and upper bounds of the interval system and divisional efficiencies. Also, the relationship between the system efficiency and the divisional efficiencies is investigated. Since the system efficiency and divisional efficiencies are expressed by interval numbers rather than by crisp values, more information is provided to make decisions.

Data envelopment analysis, interval system efficiency; interval divisional efficiency; interval data;two-level programming