Activity networks determine project performance

TL;DR

This paper reveals that project delays are influenced by the entire activity network structure, not just the critical path, using a generative model and real project data.

Contribution

It introduces a duplication-split network model that explains project schedule properties and delay propagation beyond the critical path.

Findings

Network structure influences project delays.

Critical path activities are a small fraction of total activities.

Delay propagation aligns with percolation theory in complex networks.

Abstract

Projects are characterised by activity networks with a critical path, a sequence of activities from start to end, that must be finished on time to complete the project on time. Watching over the critical path is the project manager's strategy to ensure timely project completion. This intense focus on a single path contrasts the broader complex structure of the activity network, and is due to our poor understanding on how that structure influences this critical path. Here, we use a generative model and detailed data from 77 real world projects (plus 10 billion dollars total budget) to demonstrate how this network structure forces us to look beyond the critical path. We introduce a duplication-split model of project schedules that yields (i) identical power-law in- and-out degree distributions and (ii) a vanishing fraction of critical path activities with schedule size. These predictions are corroborated in real projects. We demonstrate that the incidence of delayed activities in real projects is consistent with the expectation from percolation theory in complex networks. We conclude that delay propagation in project schedules is a network property and it is not confined to the critical path.