Many statistical technicians, particularly six sigma professionals, face this kind of problem. Not only is it difficult to explain their job to family and friends. But it’s also challenging to explain to co-workers. The problem is, we lack the understanding to keep things simple.
In this article, you’ll know what DPMO is and how it works.
As Henry Wadsworth Longfellow said, “In Character, in manner, in style, in all the things, the supreme excellence is simplicity.”
We’ll appreciate process capability more when we know WHO defines quality. Is the quality of a process or a product definite by the staff of the company?
Is it the trendy, the quality control department, engineer, or the company’s CEO?
The answer is NO, “the CUSTOMER always decides.”
Hence, to provide an exceptional product or service, we must understand what the customer wants and build products and services with the customer’s specifications. For instance, you don’t get to decide when a customer wants his Pizza delivered. And you can’t impose your ideal phone to someone who has chosen what he wants.
Suggested Read: DMAIC approach in lean six sigma
The two implications of deciding for the customer are:
Where your product fails to meet the customer’s expectations and most of the times, they return goods that don’t satisfy them. Making adjustments would cost you additional expenses while ignoring dissatisfied customers can cost you your business.
In this case, your product has more than what your customers want and this might have no impact on their experience. If you sell at the customer’s expected price, you’ll run at a loss. Selling at a higher price might make you deliver late. And you might lose your customers due to the lateness or cost.
Process capability is the measurement of how well a process is meeting consumer expectations. With competence studies, you’ll know
- how well you’re doing, relative to consumer’s specifications
- ways to progress
- if the improvements you’ve complete are working
- which suppliers are generous you the best service
Eventually, an excellent procedure capability can decrease the cost of poor quality (COPQ). The image that follows is a typical process capability road map.
Also Read: Six Sigma memes
Industries use sigma level to interpret their capability into a reporting metric. And it’s termed universal because you can analyze it from either a continuous or separate data. You can regulate the sigma level by the short term Z score. And for separate data, you’ll calculate from the defect rate.
You can also use the sigma level as a management reporting tool. You can change any capability metric to a sigma level if essential.
- Sigma level can be used to define the capability of the main metric
- For continuous data, it’s the predictable defect rate or Cp, Cpk or Cpm.
- For discrete data, this will frequently yield, DPU or DPMO
- In the course of this article, you’ll see how to calculate the sigma level for separate data.
Type of data
The following table explains the types of data
It is important to understand the difference between the data types as the calculation for process capability or sigma level changes for data types in terms of calculation as well as understanding
Defect and Defective
Any feature of a product or service that doesn’t meet the customer’s specification is a defect. While defective is the term used to qualify a product that has a defect. Let’s adopt you want to manufacture a mechanical part for an automobile. Visualize that its dimensions are exact and you made the length 12cm instead of 10cm.This product is faulty and if it’s just the length, then it has one defect. But if two dimensions are affected, it has two defects.
And so on. The number of defects that can occur in a product is known as defect opportunity (or simply opportunity). You can also say those opportunities are the only things you need to do correctly to satisfy the customer.
Each field in an insurance firm represents an opportunity. And each line of code in software is also an opportunity.
Capability for Discrete, “Count” Data
Defects per Unit (DPU): It is the ratio of the Sum of all the defects on all units to the total number of units
DPU = Sum of all the defects on all units/total number of units
You only calculate DPU when it is probable to measure multiple defects for a single unit. It works with the supposition that all “units” are identical. In other words, the opportunities for making defects are fixed.
Cases where you should use DPU include
- Multiple non-uniformities on a block of Paneer
- Numerous design mistakes during a project
- Insurance forms that can have errors in multiple fields
Defects per Opportunity (DPO)
The DPU assumes that all units are identical. And it doesn’t take into account the complexity of each unit. So, you must determine the defects per opportunity.
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The first step is to calculate the opportunity.
Let’s use the previous example. Suppose each insurance form has 50 mandatory fields. And not filling one can lead to the rebuff of the form.
DPO = (Total defects) / (Total units X Opportunities per unit)
DPO = 11 / (10 X 50)
DPO = 0.022
This means in the present process, 0.22 defects are produced per opportunity.
When the defects per opportunity become very low, organizations often fast competence in terms of defect per million opportunities in its place of DPO
DPMO = DPO * 1,000,000 (1 million)
DPMO = (Total defect / (Total units X opportunities per unit)) X 1000000
Let’s go to our earlier example again.
Here DPO = 0.022
DPMO = 0.022 * 1000000
DPMO = 22000
Hence per 1 million opportunities, the bank is making 22000 defects.