Lead time scatterplots

Lead time scatterplots are an important tool for a team working with Kanban. Sometimes these are referred to as a “Control Chart” which is often the case in manufacturing. However, in knowledge work I think it’s less about the “control” mechanism and more about using it to improve the capability of the term providing the services. Thus I usually just refer to these as “scatterplots” and if you look at the example below you can see why.

There’s quite a bit going on here, so lets look at each part in turn.

X-Axis – This contains a series dates, you can see they progress over about an 8-9 month period moving from left to right chronologically.

Y-Axis – Time in calendar days. This is the amount of time a work item took when it was completed. This is calendar days, so it includes weekends and public holidays.

Orange dots – These represent Standard class of service items. Each time an item is completed, an orange dot is added at the date of completion and the total lead time for the item.

Grey triangles – These represent Fixed date class of service items. Similarly to the orange dots, they represent when an item is completed and the lead time to completion.

Orange dotted horizontal line – This represents the 95th percentile mark for Standard class of service items. That is, 95% of the work items fall under the line and 5% above. This line is optional, plus you can add lines at different percentile’s as per your needs (eg 85%).

Grey dotted horizontal line – This represents the 95th percentile mark for Fixed date class of service items.

You may notice a few things:

  • Lead times are not necessarily uniform. This is often the case in knowledge work – thinking everything is exactly the same is a common misconception
  • Sometimes there are gaps – there may be holiday periods where there is less work going on. You should understand this as being part of the normal cycle / capability of your team.
  • Some items take a large amount of time – Often items that are blocked or have external dependencies cause work items to have their lead time blow out.
  • There are much fewer Fixed date items than standard.
  • Fixed date items have a much lower lead time

Things to look out for

  • Growing lead times – this would tend to indicate an underlying problem in the system that you need to attend to
  • Where batches are completed together – there may be some bottleneck in the process preventing things from getting done, or the items might not be independent – look at how you slice for independence.
  • In progress items – this only shows you the “Done” items, it doesn’t show you the ageing of currently open items. You can use a separate chart for this – it’s important to action problems early before it’s too late!

You don’t need a whole lot of data for this to get started. All you need is the start date and end date of each of your work items. A few years ago I did a lightnight talk at Agile Australia 2017 that talks about this. If you’re looking for a tool to help you do this, you should check out Troy Magennis’ “Throughput and Cycle Time Calculator” excel sheet in his Focused Objectives repository.

It’s good to understand the basics about how these scatterplots work. I’ve touched on some of the ways they can be used, but there’s more detail to it than that and it requires a few other charts, so I’ll save this for a future blog post.

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