Establishing Precedence Relationshi

Establishing Precedence Relationships A precedence relationship determines a sequence for undertaking activities; it specifies that one activity cannot start until a preceding activity has been completed. For example, brochures announcing a conference for executives must first be designed by the program committee (activity A) before they can be printed (activity B). In other words, activity A must precede activity B. For large projects, establishing precedence relationships is essential because incorrect or omitted precedence relationships will result in costly delays. The precedence relationships are represented by a network diagram, similar to what we used for analyzing line balancing problems (see Chapter 6, “Constraint Management”).Estimating Activity Times When the same type of activity has been done many times before, time estimates will have a relatively high degree of certainty. Several methods can be used to get time estimates in such an environment. First, statistical methods can be used if the project team has access to data on actual activity times experienced in the past (see MyOMLab Supplement H, “Measuring Output Rates,”). Second, if activity times improve with the number of replications, the times can be estimated using learning curve models (see Supplement I, “Learning Curve Analysis,” in MyOMLab). Finally, the times for first-time activities are often estimated using managerial opinions based on similar prior experiences (see Chapter 8, “Forecasting”). If the estimates involve a high degree of uncertainty, probability distributions for activity times can be used. We discuss how to incorporate uncertainty in project networks when we address risk assessment later in this chapter. For now, we assume that the activity times are known with certainty.