What does it mean to maintain a stable system, and, moreover, why does this actually matter? The short answer is that stable systems translate into predictable systems.
Predictable systems enable you to give a confident answer to the quite common question “When will this be done?”. They enable the possibility to create accurate delivery forecasts based on your past performance, thus producing highly reliable service level agreements. And, furthermore, this can be achieved with less effort and time than what would be spent using alternative approaches, like estimating your work.
The second perspective reveals the reliability of your system’s behavior. Stable systems prevent excessive work demand from sacrificing the quality of your work and relieve overburden. They help you support a healthy flow of work and stick to your commitments.
The Average Age of WIP in a Nutshell
According to Little’s Law, maintaining a stable system depends on two factors – your work in progress and your average age of work in progress. For these two metrics, the key is consistency – predictable systems are determined by keeping both your WIP and the average age of your WIP consistent.
Your WIP is the amount of work that is in progress at any given time in your process. Sticking to your WIP limits will help you maintain consistent WIP over time.
The age of an item in progress is the time that it has already spent in the workflow up until the present moment. The average age of your WIP is then calculated by dividing the sum of the ages of all your items on a certain day by the total number of items.
What does the Average Age of WIP tell us that Cycle Time doesn’t?
The average age of WIP and cycle time are essentially the same metric, only cycle time is measured against completed tasks, whereas the age of a task is a measure concerning tasks that are still in progress.
Your cycle time metric doesn’t take into account your current WIP. Although you might have a very low average cycle time, if your tasks sit and age in the process, and eventually get released at a later stage, your average cycle time will skyrocket. This is why it is so important to track your average age of WIP, and regularly compare it against your average cycle time.
Evaluate your WIP Average Age to Breed Predictability
The average age of your work is measured in days, on a daily basis – for example, if today is 4 March and an item was started on 2 March, on 2 March the item’s age was 1 day, and today, it is 3 days old.
So your average age of WIP will tell you at the present moment that, as per the example above, all your items have already spent an average of 7 days in progress. You can then compare that number to your average cycle time which is 5 days. This instantly shows you that your current WIP is disproportionately slower than your norm, and that your current work is taking more time than the time needed to finish all of the tasks so far, on average. This means that, once you release your current work, your average cycle times will almost double.
The ideal scenario is to either establish a lower WIP average age and higher cycle time, in case you strive to optimize your delivery times, or for both of these metrics to be roughly equal.
Track your WIP Average Age Trend to Cultivate Consistency
If the average age of your work stays roughly equal on a daily basis, then its trend line will be linear; neither increasing, nor decreasing over time. This means that your WIP average age is consistent.
If you find that the line is sporadic, at times increasing or decreasing dramatically, this points to an inconsistent average age and, at the root cause of these spikes, bottlenecks in the system that need to be addressed. The best way to investigate further is by examining the period with the most jumps, then going back and analyzing the tasks with the highest age from that period.
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Tips to Establish a Consistent Average Age of WIP
Evaluating and regularly assessing your WIP and your average age of WIP is the cornerstone of achieving a stable system. Here are some tips and tricks to help you achieve and sustain consistent outcomes.
Stick to your WIP Limits to Get More Done While Doing Less
WIP limits are designed to stop work from getting stuck in your process. They help you get more done rather than doing more. By applying WIP limits to your team’s Kanban board, you can improve team focus, reduce cycle times and so, ultimately, increase customer satisfaction.
When you are in a position where outstanding tasks must first be cleared, the whole team’s focus is centred on resolving bottlenecks that slow down the delivery speed. Since no new tasks can enter the system, the team’s attention is kept firmly on first finishing work that has already been started. By clearing any outstanding work before new work is begun, you facilitate the maintenance of a consistent average age of WIP.
Implement Classes of Service to Specify Different Work Type Interactions
Classes of Service (CoS) have two main purposes: to classify different work items based on their priority, and to define the way they interact with each other. Explicit policies apply to different priority levels. The policies should be determined by the project requirements, but they can also include rules, such as the order tasks should be pulled into the workflow from the backlog, plus take into account work in progress limits and resource allocation.
The main benefit of implementing Classes of Service is that special cases can be handled, without disturbing your standard workflow. In this way, critical tasks such as emergencies and hitting project milestones can be seamlessly prioritized following established policies – with each scenario, everyone on the team knows exactly what they need to do to meet their deadlines and ensure work moves forward.
Adopt FIFS to Avoid Delays and Abandoned Work
In order to stop flow dept from building up, introduce pull policies for every process state. Your team can handle work on a first come, first served (FIFS) basis.
Every task that goes onto the next process state is immediately placed at the bottom of the column. Then, once a team member has the capacity to handle new work, they pull in the task at the top of the previous column. By using this method, tasks are no longer delayed or abandoned, because each work item is processed and begun precisely in the order that it arrived – regardless of its difficulty, size or priority.
This does not mean that you should stop prioritizing your tasks. Prioritization in Kanban is very important when deciding which task should be the next one to be pulled into the process. However, once the team has pulled a task into the workflow and committed to the item, the priority is no longer taken into account and the work is processed on a FIFS basis. This approach helps to keep a constant WIP average age as it guarantees that your work enters and exits the process in a consistent manner.
Manage Your Work in Progress to Stick to your Commitments
Тhere are plenty of reasons causing tasks to get stuck in your workflow. These include internal and external blockers, neglected tasks, unclear requirements, delayed business feedback – these are just a handful of the many potential causes behind a delayed WIP.
Leaving incomplete tasks in the workflow for too long drastically increases your WIP average age. That in turn makes your system unstable and unpredictable, as it carries a risk of reduced forecasting accuracy, hindering your ability to predict delivery times for both single work items and entire projects alike.
A simple yet effective method is to introduce a new policy where a task is recategorized, becoming expedite if it’s approaching the commitment date. If you’ve agreed to deliver a task within 17 days with a 85% certainty, then the task becomes an Expedite class of service once it crosses the 70th percentile. Essentially, what you’re saying here is: “70% of our tasks have taken less time than this one to complete, so let’s focus on it in order to fulfill our commitment.”. However, keep in mind that this method generates flow dept.
Whichever approach you choose, always consider the long-term consequences of your short-term decisions.
There is a lot to be gained by keeping a closer watch on your Average Age of WIP. By managing it over time, you can establish a stable system and reap all the rewards that come with it. And the more stable your system is, the more predictable it becomes.
