Process optimisation models: Lean, Six Sigma, BPMN and when to use which

Short answer. The best-known process optimisation models are Lean, Six Sigma, BPMN, value stream mapping and the PDCA cycle. Lean removes waste, Six Sigma reduces errors and variation, BPMN records a process unambiguously, value stream mapping shows where work gets stuck and PDCA tests improvements in short rounds. In a mid-sized company you use them as tools, not as a programme.

In large organisations these models often take on a life of their own. An improvement programme with belts, templates and a steering committee, while order handling is exactly as slow as before. In a company of fifty or two hundred people there is no time for that. What you need is the way of looking. You can skip the belts and the templates.

This article belongs to process optimisation: map the process first, then the software that fits.

Lean: removing waste

Lean is a way of working that removes everything that adds no value for the customer, so that work flows without interruption. The five principles of James Womack and Daniel Jones are: define value from the customer's perspective, map the value stream, create flow, work on demand (pull) and keep improving (Lean Enterprise Institute).

Lean comes from Toyota's factories, but it works just as well in an office. There the inventory sits in a mailbox: orders waiting for someone to pick them up. And the unnecessary transport is an export from Exact Online to Excel and back.

Lean fits when your problem is lead time. Customers wait too long, quotes sit idle, an order passes five people before it leaves the building. It goes wrong when Lean turns into a hunt for minutes. Saving five minutes on a step that shouldn't exist is not an improvement.

Six Sigma and DMAIC: reducing errors and variation

Six Sigma is a method for reducing errors and variation in a process based on data. It uses the DMAIC cycle: Define (set out the problem and goal), Measure (measure how the process performs now), Analyze (find the root causes), Improve (test and implement solutions) and Control (make sure the improvement sticks) (ASQ).

Use it when the same error keeps coming back. Wrong shipping addresses, invoices with deviating amounts, returns booked differently than agreed.

Six Sigma has one hard requirement: reliable data. If your numbers come from five systems that contradict each other, you mostly measure your own fragmentation. Then the patchwork of tools has to be solved first.

Lean Six Sigma: the difference and the combination

Lean and Six Sigma ask a different question. Lean asks which steps are unnecessary and where work waits. Six Sigma asks why a step keeps going wrong. The first makes a process faster, the second more reliable.

Lean Six Sigma combines the two. For a mid-sized company the order is then logical: first take the unnecessary steps out, then make the remaining steps error-free. Do it the other way round and you perfect steps that should have been removed.

BPMN: recording a process unambiguously

BPMN (Business Process Model and Notation) is an international standard for recording business processes in a diagram, with fixed symbols for tasks, decisions, events and responsibilities. The Object Management Group maintains the standard; the current version is BPMN 2.0.2 (OMG).

BPMN improves nothing by itself. It makes a process discussable. As soon as a process fits on one page, everyone sees the same four handovers and the same loop that goes nowhere. That discussion usually delivers more than the diagram itself.

I mainly use BPMN when departments each describe the same process differently, and when software is about to be built. A BPMN diagram is the best briefing you can give a developer, because it records which decisions the software has to make and which exceptions exist. Do draw what actually happens. The ideal process comes later.

Value stream mapping: seeing where work gets stuck

Value stream mapping is a Lean technique in which you put every step from request to delivery on one map, including the waiting time between steps and the information that travels along (Lean Enterprise Institute). Unlike a regular process diagram, you also measure time. So you see how long work sits still.

That is often the biggest eye-opener. An order gets twenty minutes of actual work in total, yet it takes three days to get through. Those three days are in the waiting between steps: for an approval, for an export, for someone who is back in the office on Monday. If everyone is busy and everything still takes long, start here.

PDCA: improving in short rounds

The PDCA cycle (Plan, Do, Check, Act) is a model for testing changes in small steps. You plan an improvement, carry it out on a small scale, check the result and then roll it out more widely or adjust (ASQ). Then the cycle starts again.

It is also how I build software. Within two weeks there is a first working version, which we test with real data and then adjust. It prevents spending half a year building something the shop floor ends up using differently than intended.

Which model do you choose?

Your problem	Start with	Why
Everything takes too long	Value stream mapping, then Lean	First see where work waits, then remove the cause
The same errors keep coming back	Six Sigma (DMAIC)	Find the root cause with data
Departments describe the process differently	BPMN	One unambiguous picture as the basis for agreements
You are about to have software built	BPMN	Decisions and exceptions are fixed before building starts
You want to keep improving after the first round	PDCA	Small, testable steps instead of one big project

The model is not the goal

None of these models removes the re-typing between your web shop and your bookkeeping. They show that it exists and what it costs. After that something still has to happen: remove a step, configure a package differently, connect systems or build something. How to make that choice is worked out in off-the-shelf, integrate or custom.