Understanding defect based six sigma metrics: DPO, DPMO, PPM, DPU, Yield

DPO, DPMO, PPM, DPU Definitions – Six Sigma Defect Metrics

What Is DPO? What Is DPMO?

A unit of product can be defective if it contains one or more defects. A unit of product can have more than one opportunity to have a defect.

  • Determine all the possible opportunities for problems
  • Pare the list down by excluding rare events, grouping similar defect types, and avoiding the trivial
  • Define opportunities consistently between different locations

Proportion Defective (p):

p = Number Of Defective Units / Total Number of Product Units

Yield ( Y1st-pass or Yfinal or RTY)

Y = 1 – p The Yield proportion can converted to a sigma value using the Z tables

Defects Per Unit – DPU, or u in SPC

DPU = Number Of Defects / Total Number Of Product Units The probability of getting ‘r’ defects in a sample having a given dpu rate can be predicted with the Poisson Distribution.

Defects Per Opportunity – DPO

DPO = no. of defects / (no. of units X no. of defect opportunities per unit)

Defects Per Million Opportunities (DPMO, or PPM)

DPMO = dpo x 1,000,000 Defects Per Million Opportunities or DPMO can be then converted to sigma & equivalent Cp values in the next page. The DPMO, DPM, Sample Size, CI Calculator will help you calculate the metrics.

If there are 9 defects among 150 invoices, and there are 8 opportunities for errors for every invoice, what is the dpmo? dpu = no. of defects / total no. of product units = 9/150 = .06 dpu dpo = no. of defects / (no. of units X no. of defect oppurtunities per unit) = 9/(150 X 8) = .0075 dpo dmpo = dpo x 1,000,000 = .0075 X 1,000,000 = 7,500 dpmo What are the equivalent Sigma and CP values? See Sigma Table.

Converting Yield to sigma & Cp Metrics – Example

Given: a proportion defective of 1%

  • Yield = 1 – p = .990
  • Z Table value for .990 = 2.32σ
  • Estimate process capability by adding 1.5 σ to reflect the ‘real-world’ shift in the process mean 2.32σ + 1.5σ = 3.82σ
  • This σ value can be converted to an equivalent CP by dividing it by 3σ : CP = 3.82σ/3σ = 1.27 Note: Cpk cannot be estimated by this method

Six Sigma Capability Improvement

SixSigma-Capability-Improvement

Sigma Table

Yield dpmo Sigma (σ) Cp Equiv. COPQ (Cost of Poor Quality)
.840 160,000 2.50 0.83 40%
.870 130,000 2.63 0.88
.900 100,000 2.78 0.93
.930 70,000 2.97 0.99
.935 65,000 3.01 1.00
.940 60,000 3.05 1.02
.945 55,000 3.10 1.03 30%
.950 50,000 3.14 1.05
.955 45,000 3.20 1.06
.960 40,000 3.25 1.08
.965 35,000 3.31 1.10
.970 30,000 3.38 1.13
.975 25,000 3.46 1.15
.980 20,000 3.55 1.18 20%
.985 15,000 3.67 1.22
.990 10,000 3.82 1.27
.995 5,000 4.07 1.36
.998 2,000 4.37 1.46
.999 1,000 4.60 1.53 10%
.9995 500 4.79 1.60
.99975 250 4.98 1.66 5%
.9999 100 5.22 1.74
.99998 20 5.61 1.87
.9999966 3.4 6.00 2.00

Our free  DPMO, DPM, Sample Size, CI Calculator will help you calculate the metrics.

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