In a series of posts I’m going to examine some of the claimed benefits of agile methods – are they justified? My first post looked at the cost of development with agile, the second discussed speed. while the third addressed quality. Here I look at claims of un-predictability of agile.
What do we mean when we say agile methods sacrifice predictability for adaptability? Here I want to explore this commonly held belief – is it true?
In this context, predictability normally means the ability to deliver to a predetermined plan – predictable from the customer point of view. The scope agreed is delivered with the necessary quality at the time and cost agreed.
But research shows that waterfall very rarely achieves this objective – in fact the record for plan-driven approaches is woeful! A now famous Standish report states that 31% of projects were cancelled before completion, while in 53% costs nearly doubled the original budget. In fact only 16% came in on time and on budget. This report was from 1995 – when plan-driven was well established and agile methods had yet to make their appearance.
I would argue that in contrast agile methods bring predictability in several ways:
1) Timeboxed – Because agile treats scope rather than time as variable, ‘something’ will be delivered at the pre-determined milestone – the schedule does not slip.
2) Agile addresses high risk items early, like testing and end to end integration. These often prove to be the reasons plan-driven methods are so un-predictable.
3) Even if some scope is not delivered at the planned milestone, agile uses prioritisation by value to ensure the most important features are delivered (45% of features are never used according to the same Standish report)
4) Agile borrows from queueing theory to devise techniques to reduce variability in the development process – smoothing work flow through small, equally sized user stories greatly reduces queuing time and bottleneck formation in the process, delivering more reliable throughput.
5) By delivering potentially releasable code in each iteration, agile provides more visibility into real progress compared to the plan-driven approaches – this provides a more reliable basis for stakeholders to revise plans based on the reality of the project rather than any now incorrect plan.
6) Agile methods use inspect and adapt to adjust plans to emerging reality – regular reality checks mean more reliable predictions of milestone deliveries are possible. In systems engineering terminology, such closed-loop systems are less reliant on every component of the system working in order to be predictable – instead they can compensate for unreliable components.
7) Agile methods encourage parallel work on various tasks and user stories – rather than analysis preceding development followed by test, these are performed concurrently. Again, queueing theory shows us that this greatly reduces the variability of any process thereby increasing predictability.
Plan-driven methods can lend an illusion of control and predictability – and can serve political or covert roles by avoiding ‘whole-team’ accountability. But both experience and theory highlight that predictability is, contrary to common belief, not their strong-point.
