Exploring applicability of Theory of Constraints to projects: Critical Chain Project Management and beyond

Abstract

Theory of Constraints (TOC) suggests focusing on the core constraint as the leverage point in any system. Critical Chain Project Management (CCPM), as an application of TOC to project management, has been a controversial topic. On the one hand, CCPM has made dramatic improvement in some contexts, and on the other hand, it has been criticised for its lack of applicability to all projects. However, no clear boundary has been yet defined for CCPM applicability. This research set out to articulate the boundaries of CCPM’s applicability and extend the application of TOC beyond those boundaries.

According to TOC, the core constraint prevents the system from achieving more of its goal. CCPM specifically suggests that the core constraint in every single project is the longest chain of dependent activities. How did CCPM arrive at this very specific definition of the constraint? This research re-examines CCPM against empirical cases.

The above examination required an in-depth analysis of both the theoretical assumptions of CCPM and the empirical reality of the projects. The abductive process in this research facilitated an iterative learning loop between theory and empirical study. The research is based on a multi-case study consisting of a total of 10 cases from a diverse range of industries. The literature analysis was complemented by text mining of a comprehensive CCPM database using NVivo and Leximancer software.

CCPM assumes that a project’s goal has a predefined and fixed value which is set at the beginning of the project. While several projects in the case study research did exhibit this characteristic, there were also projects in which achieving more of the goal within the same project was possible. The research also found that in some projects the baton (the project) was sequentially passed between project actors, while in other projects a dedicated team carried the baton all the way through. This re-examination of CCPM led to a 2x2 constraint classification model.

Four cases, each occupying one quadrant of the above model were further analysed. The findings suggest that, when the value of the project is fixed and the project is executed by a non-dedicated team, the constraint is the longest chain of dependent activities. However, if a fixed-value project is executed by a dedicated team, the system ‘is’ the team and therefore its weakest link is the most constrained resource. The findings also suggest that projects with variable value are often confronted by various aspects of scope formulation, irrespective of their team type. Analysis also explored the use of alternative TOC solutions in each case.

The above constraint classification model predicts that applicability of CCPM requires fixed value of the output, sequential workflow, and a non-dedicated team. Further analysis suggests two other prerequisites to CCPM applicability: unity of purpose and urgency.

This research stands on the shoulders of a giant: CCPM. The findings challenge CCPM’s assumptions. Through this process of assumption-challenging, the research extends and enhances the application of TOC to the broader project management realm.