DPMO (defects per million opportunities) - Key word being OPPORTUNITIES

[tww11]

I keep getting conflicting information on DPMO. The key word being OPPORTUNITIES. I think people are confusing DPMO and PPM. Some people think it tells them how many parts out of 1million have defects, but we are not measuring parts defective in DPMO. Does the 1,000,000 in PPM mean 1 million parts and the 1,000,000 im DPMO means 1 million opportunites?

Here is my interpretation:

1000 units, 5 defects, 2 opportunites for defects per unit

1000 units X 2 opps per unit= 2000 total opportunities

5 defects / 2000 total opportunities= .0025

So, every opportunity shares .0025 of a defect.

Now, I take .0025 X 1,000,000 opportunites (not parts)= 2500 defects per million opportunites

This tells me nothing about the amount of parts that have defects. That is what PPM is for. This only tells me how many defects I will have over 1million opportunities. Is this right?

[Desara01]

Hi tww - hope you're well this evening. What a great question! And you are, in fact correct. Good for you to question the numbers!

DPMO allows us to examine each unit and determine how many possible ways it can fail. PPM looks at a P/F for each part. They will be the same number if you consider the number of opportunities for failure to be - you guessed it - 1. Here's an example. A company is counting inventory. They scan in barcodes - either the scan works or it doesn't. Now, the numbers are one and the same. If, however, I were scanning for 6 pieces of information, now the numbers are considerable different, yes?

Both numbers can/should be important in most situations - management needs to know the acceptable "pass" rate - that's ppm, right? But DPMO might tell a very different story. If there are 5 opps to fail, and I'm failing 4/5 most of the time - well that's obviously more severe - or requires a different attack plan - vs. if I'm failing on one recurring characteristc, right?

When you calculate DPMO, just make sure you are very clear on what the "opportunities for failure" are, get agreement from management, and remain consistent as you track your improvement efforts.

One more thought/observation: I have seen DPMO manipulated by management to make the number look better by not counting all the opportunities. I've also seen the number manipulated by Quality Managers in the other direction.

Key point: create a clear operational definition of the metric and ensure it's communicated and understood. Then you can start to make good decision. Dr. Deming said something like this - Data only has meaning when we know how it was counted/collected. Or something to that effect. If you want more info on operational definitions, let me know.

Hopes this helps. Cheers!

[Miner]

Excellent response by Desara01. The key take-away is the need for an operational definition for "Opportunity". Keep it as simple as possible, such as part count for circuit boards.

[Stijloor]

In Reply to Parent Post by Desara01

Dr. Deming said something like this - Data only has meaning when we know how it was counted/collected. Or something to that effect.

Dr. Deming quote:

When information is obtained, or data is measured, the method, or process used to gather information, greatly affects the results.

Thank you for mentioning the concept of "operational definition" in your post!

Stijloor.

[Desara01]

thank you stil for the quote - I was in the ballpark, anyway :-)

[Stijloor]

In Reply to Parent Post by Desara01

thank you stil for the quote - I was in the ballpark, anyway :-)

Yes you were! Yes, Dr. Deming...what a legacy and wisdom he left... His lessons are as fresh and are as current today as they were when he started his long and impressive career. I still refer to "Out of the Crisis" and "The New Economics" and continue to gain valuable insights.

Learning never ends.

Stijloor.

[tww11]

I'm doing very well. Thank you. I hope you are too.

Thank you very much for the answers. The more I learn about Six Sigma, the more I realize that alot of people don't know what they are doing. It was frustrating me because alot of people mixed PPM and DPMO together or think its the same metric. Maybe when the opportunity is 1 like you said.

Well, I'm taking a study course and it states "As a yield measurement, DPMO indicates the number of defects in a process observed during a production of one million units."

This is the statement that got me confused. They say units, but they have to mean opportunities right? Otherwise they would be comparing apples to oranges. If you multiply the average defect per opportunity by 1 million parts, how would that tell you how many defects per opportunity I have?

[tww11]

Here's another example of why people are confused. This is something I found online. Read the last sentence below. Why would they say this when it's not the same metric?


2. Defects per Million Opportunities, or DPMO � indicates how many defects would arise if there were one million opportunities. In manufacturing, DPMO is often called PPM (parts per million).