Purpose
The flow-based perspective of Kanban can enhance and complement the Scrum framework and its implementation. Teams can add complementary Kanban practices whether they are just starting to use Scrum or have been using it all along.
The Kanban Guide for Scrum Teams is the result of a collaboration between members of the Scrum.org community and leaders of the Kanban community. Together, they stand behind The Kanban Guide for Scrum Teams. It is their shared belief that professional product development practitioners can benefit from the application of Kanban together with Scrum.
Relation to the Scrum Guide
This guide does not replace or discount any part of The Scrum Guide. It is designed to enhance and expand the practices of Scrum. This guide assumes the reader is operating a process using the Scrum framework. Therefore, The Scrum Guide applies in its entirety
Definition of Kanban
Kanban (n): a strategy for optimizing the flow of value through a process that uses a visual, workin-progress limited pull system.
Kanban with Scrum Theory
Flow and Empiricism
Central to the definition of Kanban is the concept of flow. Flow is the movement of value throughout the product development system. Kanban optimizes flow by improving the overall efficiency, effectiveness, and predictability of a process.
Optimizing flow in a Scrum context requires defining what flow means in Scrum. Scrum is founded on empirical process control theory, or empiricism. Key to empirical process control is the frequency of the transparency, inspection, and adaptation cycle - which we can also describe as the Cycle Time through the feedback loop.
When Kanban practices are applied to Scrum, they provide a focus on improving the flow through the feedback loop; optimizing transparency and the frequency of inspection and adaptation for both the product and the process.
The Basic Metrics of Flow
The four basic metrics of flow that Scrum Teams using Kanban need to track are as follows:
- Work in Progress (WIP): The number of work items started but not finished. The team can use the WIP metric to provide transparency about their progress towards reducing their WIP and improving their flow. Note that there is a difference between the WIP metric and the policies a Scrum Team uses to limit WIP.
- Cycle Time: The amount of elapsed time between when a work item starts and when a work item finishes.
- Work Item Age: The amount of time between when a work item started and the current time. This applies only to items that are still in progress.
- Throughput: The number of work items finished per unit of time.
Little’s Law - The Key to Governing Flow
A key tenet governing flow theory is Little’s Law, which is a guideline that establishes the following relationship:
Little’s Law reveals that in general, for a given process with a given throughput, the more things that you work on at any given time (on average), the longer it is going to take to finish those things (on average).
If cycle times are too long, the first action Scrum Teams should consider is lowering WIP. Most of the other elements of Kanban are built upon the relationship between WIP and Cycle Time.
Little's Law also shows us how flow theory relies on empiricism by using flow metrics and data to gain transparency into historical flow and then using that data to inform flow inspection and adaptation experiments.
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