Project Management

Why doesn't Disciplined Agile use the term "predictive"?

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Quick answer

The term predictive is deceptive.


Detailed answer

In the Disciplined Agile (DA) tool kit we use the term traditional or serial, rather than predictive or waterfall, to refer to the classic/linear ways of working.  We feel that predictive is deceptive, more on this in a minute, and waterfall to be insulting (albeit still in common use within the IT community).  Furthermore, we're starting to move away from using traditional as we're now seeing a generation of practitioners who feel that some of the older agile approaches, in particular Scrum, are traditional ways of working.

There are several reasons for why we feel the term "predictive" to be deceptive:

  1. "Predictive" implies predictable.  Predictive is defined as "relating to the ability to predict" whereas predictable is "something that happens in a way or at a time that you know about before it happens."  Something that is predictable is a sure thing, yet something that is predictive is not. This is an important difference, particularly given that we know that projects aren't completely predictable - otherwise we wouldn't need risk management.
  2. "Predictive" approaches to IT projects are a poor choice in most cases.  Years ago I led a study for Dr. Dobb's Journal that investigated the effectiveness of different approaches (agile, lean, iterative, ad hoc, and traditional) to IT projects.  We found that traditional strategies were less effective in practice than agile and lean approaches, and we weren't the only ones to have found this.  We also investigated what was initially predicted at the beginning of the project and what actually happened by the end of the project, and once again traditional approaches didn't do as well as agile & lean.  BUT, I must stress that the study focus was on IT projects only, not on projects in general.  
  3. "Predictive" approaches to intangible projects are likely a poor choice  DDJ found, in several studies in fact, that "predictive" strategies were less predictable in practice than agile/lean approaches in IT.  I highly suspect that this is true of intangible projects in general although do not have hard data to back up that claim.  We need to investigate this.
  4. "Predictive" approaches to tangible projects are likely a good choice, but I suspect we can do better.  I suspect that "predictive" approaches are more appropriate for tangible projects, such as building houses or buildings, than agile/lean approaches.  I also believe that a hybrid approach combining the best from traditional, agile, and lean strategies is likely better than traditional alone. Having said this, as with the previous point, I don't know of any research that has compared the various project management paradigms for tangible projects, so this too is something we need to investigate.

In short, we know that "predictive" is a deceptive term for a large category of projects and suspect this to be true for other project types.  As a result the only use of the term predictive in DA is to tell you that we don't use it.


Posted by Scott Ambler on: November 09, 2020 12:38 PM | Permalink

Comments (9)

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Eduin Fernando Valdes Alvarado Project Manager| F y F Fabricamos Futuro Villavicencio, Meta, Colombia
Very interesting, thanks for sharing

Kiron Bondale Mentor| World Class Productivity Inc. Welland, Ontario, Canada
Scott, while I'd agree that we can't predict 100% of a project's outcomes, we can assure predictability with regards to specific constraints (e.g. time, cost) so long as we allow adaptability on others.


Carla Krieger Enterpries and Team Agile Coach| Grupo Globo Niteroi, Rj, Brazil
A few weeks ago I spoke in a Webinar about the big difference between prediction and probability, highlighting the use of methods like Monte Carlo based on historical data like Lead Time and that we can work on our initiatives in any approach (traditional or adaptive), but thinking on how to increase the forecast accuracy , not prediction.
Nice post, Scott! Thanks!

Scott Ambler Consulting Methodologist| Ambysoft Inc. Toronto, Ontario, Canada
@Kiron, agreed, but that's arguably the entire problem. What we found at DDJ was that at the beginning of a project the team would promise they would deliver X, for a cost of Y, by date Z. Sometimes those estimates would be ranged, sometimes not. And then the project would progress and stuff would happen. By the end of the project, the scope delivered was X', the cost was Y', and the date Z'. Sometimes X' was reasonably close to X and sometimes not. The study found that the greatest chance of one of X, Y, or Z being significantly different at the end of the project was with the "predictive" strategies. So "predictive" proved to be the least predictable in practice.

Kiron Bondale Mentor| World Class Productivity Inc. Welland, Ontario, Canada
@Scott - absolutely! Locking down all three legs of the iron triangle prematurely is insanity! But it was perfectly reasonable to lock down at least one of those so long as the customer and key stakeholders are willing to be flexible on the others. Where this breaks down is when you get into highly complex or highly innovative projects where the pre-defined constraint is simply unachievable even to deliver an MBI.

Some degree of predictability is desirable in delivery, otherwise we won't gain the trust of our stakeholders.


Muhammad Mohsin Rashid Manager PMO| Symbo Ltd Lahore, Punjab, Pakistan
Hope PMBOK will follow the same approach in coming edition as well

Syed Arshad Ali Ahmed General Systems Analyst| SCC Hyderabad, Telengana, India
I completely agree with @Kiron...

However, a hybrid approach clubbing together the best from traditional, agile, and lean strategies is the way to go forward....


Abolfazl Yousefi Darestani Manager, Quality and Continuous Improvement| Hörmann-TNR Industrial Doors Newmarket, Ontario, Canada
Thank you for sharing.

ASHISH SADEKAR Founder and Partner| ProThoughts Mumbai, India
Thanks for sharing.
Though I believe that predictive is embedded in every approach the things we do. The degree of predictability may be minimum say in Lean, but we do that. The idea is how to predict - based on what and how it can give a reasonable picture?

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