In the Disciplined Agile (DA) tool kit we use the term serial and sometimes traditional, 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 moving 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 also traditional ways of working.
There are several reasons for why we feel the term "predictive" to be deceptive:
- "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 change or risk management. Furthermore, PMI's definition of a project is "a temporary endeavor to create a unique product or service." The fact that our outcome is unique should tell us the journey there cannot be fully predictable because we have not done it before.
- "Predictive" approaches to IT projects are a poor choice in most cases. Several years ago, a study for Dr. Dobb's Journal investigated the effectiveness of different approaches (agile, lean, iterative, ad hoc, and traditional) to IT projects. It found that traditional strategies were less effective in practice than agile and lean approaches. It also investigated what was initially predicted at the beginning of the project and then what happened by the end of the project, and once again traditional approaches didn't do as well as agile or lean. Once again, this study focused on IT projects only, not on projects in general.
- "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 for IT projects. We suspect that this is true of intangible projects in general, although do not have hard data to back up that claim.
- "Predictive" approaches to tangible projects are often a good choice, but hybrid can often be better. We suspect that "predictive" approaches are more appropriate for tangible projects, such as building houses or buildings, than agile approaches. We also believe that a hybrid approach combining the best from traditional, agile, and lean strategies will prove better than traditional alone.
The term serial doesn’t suffer from the challenges with predictive. Furthermore, it captures the essence of the strategy, to work through a progression of phases or stages in a linear manner. Yes, there will often be feedback cycles to previous stages, often due to quality problems or changes in your situation, but for the most part the work proceeds in a serial manner.