A surrogate indicator of criticality for stochastic project networks L. V. Tavares, J. A. Ferreira and J. S. Coelho CESUR-IST, Av. Rovisco Pais, 1049-001 Lisbon, Portugal E-mails: lavt@civil.ist.utl.pt [Tavares]; antunes.ferreira@cesur.civil.ist.utl.pt [Ferreira]; jcoelho@siweb.info [Coelho] Received 20 May 2002; received in revised form 14 March 2003; accepted 10 April 2003 Abstract The study of the delay that can be caused by any activity of a stochastic project network is a key topic because of the increasing importance of risk and time control in project management. The main concept adopted for this purpose has been the notion of critical activity developed for deterministic project networks but, in this paper, the inadequacy of the concept critical activity for stochastic project networks is shown and a new surrogate indicator of criticality (SIC) is built, using a regression model applied to a large set of generated project networks. This new indicator explains more than 90% of the initial variance estimated for more than 80,000 activities belonging to a wide range of project networks (580 nets), with very different morphological types. Keywords: Stochastic project network; risk; criticality. Introduction The concept of project network has been the main seed for the development of the whole area of project management and project scheduling, since the early developments of the critical path method (CPM) and the project evaluation review technique ( PERT) (Battersby, 1967; Clark, 1962). Such concepts support the development of scientific knowledge about each project along different lines, namely:  analytical decomposition of the project into interdependent components (so called activities);  analytical description of the precedence structure;  identification of the activities with a higher potential to delay the total duration of the project, assuming that the duration of each activity is a random variable (stochastic project networks). Intl. Trans. in Op. Res. 11 (2004) 193–202 INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH r 2004 International Federation of Operational Research Societies. Published by Blackwell Publishing Ltd.