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any companies are realizing that delivery of products as scheduled is one aspect of measuring the success of new product introduction [1][2][3] . Unfortunately, in spite of the intensive use of computer assisted design tools, such as CAD and expert systems, managers of engineering design projects are still facing the problem of severe schedule and cost overruns. In published papers, the reported average schedule overrun ranges from 41% to 258%, and cost overrun ranges from 97% to 151% 3,4 . The following points indicate why better estimation of effort and duration of design projects is so important: ΒΌ in some situations, cost or schedule overruns lead to project termination 5 ; ΒΌ schedule overrun increases the risk of product obsolescence due to the increased risk of missing the market window [5][6][7] . In many cases this means a project failure. According to Evans 8 , delay is deadly. In the auto industry, one study indicates that each day of delay costs an automobile firm over $1 million in lost profits 9 ; and ΒΌ an initial delay in a project can engender further delays. Once a project is late, one or both of the following measures are usually taken: 1 Maidique, M A and Zirger, B J 'A study of success and failure in product innovation: the case of the U.S. electronics industry ' IEEE Transactions on Engineering Management Vol EM-31 (1984) pp 192-193 2 Stalk, G and Hout, T Competing against time Collier Mac- millan, London (1990) 3 Murmann, P A 'Expected development time reductions in the German mechanical engineering industry'