YOU DID IT! You adhered to the rigor of Lean Six Sigma, following the DMAIC process to successfully improve your process. You did improve your process, right? How can you prove this? Cue your primary metric… 

Overview: What is a primary metric? 

A primary metric is a direct output characteristic of a process. It is something Six Sigma practitioners can directly influence and is therefore used to measure project success. Much like Highlander, “there can only be one.” Some examples of primary process metrics include defect rate, first time yield, or process cycle time

3 benefits of a primary metric

By directly measuring the process output, the primary metric provides several benefits to Six Sigma practitioners as they work to improve processes. 

1. It makes the process objective

By assigning a numeric system to monitor the process, it’s easier to gauge how efficiently the process is running and whether or not it’s meeting the customer requirements. This removes the ambiguity of vague customer requirements such as “good quality.”

2. It allows the creation of an improvement goal

If the numbers measuring the process are not meeting customer requirements, a specific target can be set for what needs to be achieved to meet those requirements. Having this improvement goal expressed as a number makes it easier to understand what is needed to ensure the process is where it needs to be compared to words such as “better.”

3. It enables feedback loops

Once the ideal state of the process is determined, the primary metric will gauge whether the process is meeting that target. If the numbers look good, no changes to the process are required. However, if the numbers fall below target, this triggers the need for adjustment to make sure the process continues to run as desired. 

Why is a primary metric important to understand? 

Since the primary metric is used to measure project success, there are a few things that are important to understand about it. 

It sets the stage for a successful project

Without fully understanding the process and determining the right primary metric, it’s difficult to make a plan for how to improve an under-performing process. Understanding the primary metric is critical to running a project designed to improve the process.

Many stakeholders rely on the primary metric

Everyone from line operators to business leaders can use the data associated with the primary metric to understand baseline and ideal-state process performance. Understanding this is important to make sure everyone is speaking the same language when referencing a given process.  

A process can have many metrics

Because there can be many metrics associated with a process, it’s important to understand which one is the primary metric as opposed to a secondary metric. The primary metric is what ultimately determines whether a process is meeting customer requirements, and it measures the success of improvement efforts.  

An industry example of a primary metric

Let’s say you work in the inks business, making batching of liquid color for screen-printing applications. There are a lot of materials that go into making a batch of ink, and if the batch is incorrectly mixed, there are rework or scrap costs associated with either fixing it or making a new one. 

It’s important that you make these batches right the first time. How can you calculate how well your plant is doing this? First pass yield is often chosen as a primary metric in the manufacturing industry because it helps measure quality, production performance, and the success of continuous improvement activities.

First pass yield = [Number of product without error] / [Total number of products]

At your site, you produce 40 batches of ink per day. However, you’ve noticed that only 30 of them make it all the way to shipping without any problems.

First pass yield = 30 / 40 = 75%

Now that you understand your current first pass yield is only 75%, you can set an improvement goal and measure how well you are doing toward meeting that new target.

Defects are another area that can often serve as the primary metric. Consider what can happen if you don’t start out with the appropriate primary metric and how you can get your project back on track.

3 best practices when thinking about your primary metric 

Since the primary metric is the ultimate measure of project success, it’s important to get it right. There are a few ways you can ensure that you choose the appropriate primary metric for your Six Sigma project.

1. Work with the team when setting the primary metric

When working on an improvement project, the primary metric must be aligned with the problem statement determined by the team. As such, it’s important to continue working with the team to make sure the appropriate metric is selected. 

2. Understand the organization’s strategic goals

The primary metric is a gauge for what progress has been made towards achieving the stated goal. When looking to reach this goal, it’s important to understand how that fits into the larger plan of the organization to make sure that achieving it moves the organization in the right direction.

3. Aim to tie outcome to inputs

As a direct output characteristic, the primary metric shows the overall outcome of a given process. When evaluating the primary metric, it is important to understand it in the context of which inputs have the biggest impact. This allows practitioners to make targeted improvement efforts by pulling the lever(s) that will show the best results.

Frequently Asked Questions (FAQ) about the primary metric

How do you determine the primary metric?

Make sure the primary metric is expressed as a number and has data that can be tracked regularly. If the metric you’re considering does not meet these criteria, it should not be your primary metric. Also consider the above best practices when selecting your primary metric.

What are some common Six Sigma metrics?

Key categories for Six Sigma metrics are productivity, people, safety, and quality. The goal of Six Sigma projects is to maintain statistical process control. Some of the most common metrics for this include: defects per unit (DPU), defects per million opportunities (DPMU), first pass yield (FPY), and others. 

How often should the primary metric be monitored?

The frequency at which the primary metric is measured depends on what it is as well as the project timeline. You want to make sure you have enough data to make a sound decision, but data collection that requires a long wait time may slow down your project progress.

Primary metrics: The measure of success

Now that you understand what a primary metric is and why it’s important, go take another look at your processes. How effectively are they operating? Did you meet your improvement goals? Having an objective number to monitor will greatly help you work towards and achieve process success to meet your customer requirements.

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