And old European proverb says ‘all roads lead to Rome’ meaning that different paths can take one to the same goal. The same is true for project delivery. There are different project management methodologies with a proven track record. The question though is how do you want to reach your goal? A friend of mine walked to Rome. I prefer a bicycle, and my wife prefers a plane. Depending on what you want to achieve you can choose different means of transport. The same is true for project delivery and there are different project management methodologies to choose from. While comparing every aspect of a waterfall and Agile methodology would be zooming in too much detail, it is interesting exploring the differences in guiding principles.

Waterfall principles
While PMBok is widely used in the US and Canada, in Europe the de facto (waterfall) project management methodology is PRINCE2. PRINCE2 (acronym for PRojects IN Controlled Environments) has a process-based approach for effective project management established in 1989 by the UK government. It moved to the public domain and offers non-proprietorial best practice guidance on project management.

In PRINCE2 much is defined upfront and plan-based, and remains focused on the original Business Case throughout the project life cycle. The 7 key principles are the ‘guiding obligations and good practices which determine whether the project is genuinely being managed using PRINCE2′ and are as follows:

  1. Continued business justification
  2. Learn from experience
  3. Defined Roles and Responsibilities
  4. Manage by stages
  5. Manage by exception
  6. Focus on product
  7. Tailor to suit the project environment

There is a strong emphasis on dividing the project into manageable and controllable stages. ‘Everything’ is ‘defined’ at project start and the project stages are generally progressing from Design to Build, Test, Deploy and Support. A Business Case is created in ‘Starting Up a project’ detailing timescales, costs, benefits and risks. PRINCE2 works with Tolerances, set up front, which allow for permissible deviation.

Agile principles
As a agile delivery framework, Scrum is founded on empirical process control theory, called empiricism. Empiricism asserts that knowledge comes from experience and that decisions could be best based on what is known. Scrum employs an iterative and incremental approach to optimize predictability and control project risk. These three pillars uphold every implementation of empirical process control:

  1. Transparency
  2. Inspection
  3. Adaptation

Defined versus Empirical
Walking to Rome or flying the same distance both have their pro’s and con’s. Likewise, there are different delivery models based on different principles. Some differences between defined and empirical are listed below.

Defined Empirical 
Work and outcomes are understood before execution Frequent inspection and adaptation occurs as work proceeds
Given a well-defined set of inputs, the same outputs are generated every time Processes are accepted as imperfectly defined
Follow the pre-determined steps to get known results Outputs are often unpredictable and unrepeatable

Defined is great for relative simple problems like production lines where you can fix scope and budget, but unlikely time, by documenting all requirements and output upfront. The Project Manager authorises Stage Work Packages based on the Project Initiation Document and creates an End Stage Report summarising the actuals from the current stage and revise project forecast. The Project Manager can do this only because the project team can break down the entire deliverable to a level where it can estimate time required. However, a predictive approach will not work in complex environments.

Where budget and time are fixed, but scope is flexible (the unknown) an empirical approach works best. It creates incremental deliverables in short-term and manageable Sprints, independent of an overarching plan. This means that agile projects are more responsive to changes in project environment and customer / business requirements. The complete Product Backlog is not defined in detail upfront as the Product Owner inspects and adapts requirements throughout the project life cycle. Business value is continuously evaluated as customer requirements may change and technology will evolve. You could argue that a Sprint is a mini predictive project and where scope is fixed at the last possible moment before delivery.

Which one to choose depends on your business characteristics and needs such as customer requirements and time to market. In addition, it also depends on your organisational capabilities; not everyone can work with an unpredictable outcome.


References and copyrights:
Interesting read PMBok versus PRINCE2: