What it means
A supplier can pass this month's inspection and still be deteriorating over a longer stretch, so trending repeated measurements helps catch the change before it becomes a severe production or customer problem. Choose a quality measure linked to the decision: defective parts per million works for repeated component receipts, while project services may need documented acceptance failures or rework hours.
ASQ discusses incoming defect targets and defective parts per million for comparable products, and a target helps, but a trend can show deterioration before the target is crossed. Define what counts as a defect, since cosmetic blemishes, safety failures and missing documentation have different effects, and track severity separately where a single combined count would hide serious problems.
Record inspected units and the sampling plan, because ten defects from a million pieces differ from ten defects in a hundred, and changing inspection intensity can make recorded quality move even if the underlying process is unchanged. An illustrative incoming defect rate is defective units divided by units inspected times one million, so 12 defective units among 100,000 inspected is 120 defective units per million inspected.
Oracle's supplier-performance documentation provides quality performance alongside on-time, quantity and purchase-order receipt measures, so quality belongs in a broader supplier review rather than as a single isolated score. Compare like with like, because a new, difficult product variant may increase defects while established products remain stable, so break out relevant item families and production sites.
Look at time as well as volume: monthly results can be noisy for small suppliers and quarterly rolling views may clarify the direction, but a rolling average should not conceal a sudden critical defect. Keep traceability through lot number, receipt date, supplier site and defect type, since a total count without identifiers is hard to investigate or contain.
Include discovered-later defects carefully, because a component may pass incoming inspection but fail during assembly or at a customer site, so link it to its source and note the delay between receipt and discovery. Separate detection from cause, since more rejects may reflect better testing, a supplier process change, shipping damage or a specification change, and the team should investigate before assigning fault.
Record the financial effect, because scrap, rework, line stoppages and warranty claims can turn a small defect count into a large cost, while minor flaws may have limited commercial effect. Use control rules appropriate to the process: one bad month is a signal to inspect, not always a trend, whereas consecutive changes, a process shift or an unusual critical defect can warrant distinct responses.
Ask the supplier for a corrective-action plan when evidence supports a process issue, specifying the affected lots, suspected causes and a way to verify the fix in later deliveries. Do not rely on self-reported quality alone, because supplier certificates and process data are useful but receiving inspection and downstream outcomes test whether they translate into acceptable goods, and rushing a supplier to meet a launch may increase rejects.
Watch small denominators, since one defect in a small lot can generate a dramatic per-million rate, so always show the raw numerator and inspected volume, and review after any change in tooling, raw material or site by comparing pre-change and post-change receipts while respecting the different mix. For an owner, supplier quality trend is an early-warning view of repeat performance that needs consistent measurement and follow-up, not a monthly percentage printed without context.
In practice
Real-world examples.
Example
Twelve defects among 100,000 inspected units produce 120 per million. The buyer records the inspected volume next to the rate so the figure can be compared with later months. It also logs whether any of the twelve were safety-related.
Example
A new product variant is separated from the established component trend. The buyer sees that the established parts are stable while the variant has a higher reject rate. This directs the supplier conversation to the new tooling rather than the whole range.
Example
A later assembly failure is traced to its received supplier lot. The team links the failure to the original receipt date and notes the weeks between receipt and discovery. The trend report then includes the discovered-later defect in the right period.
Formula
Calculation
Illustrative defective units per million inspected = defective units / inspected units x 1,000,000.
Worked example. 12 / 100,000 x 1,000,000 = 120 defective units per million inspected.
To see a trend, repeat the same calculation each month under the same inspection rule. If the next month has 30 defective units among 150,000 inspected, the rate is 30 / 150,000 x 1,000,000 = 200 per million. The rate has risen from 120 to 200, an increase of 80 per million, which is a signal to check mix, sample size and defect severity before drawing conclusions.Case study
Seen in the real world.
In this entirely fictional example, Cedar Devices sees three months of rising defects from one production site. It checks inspection consistency and product mix, then works with the supplier on a tooling fix. Later incoming lots are measured against the same rule before the team calls the trend improved. Cedar's quality lead first confirmed that the same inspector instructions and sample sizes had been used in all three months.
Only then did the team accept that the rise was real rather than a change in how closely the goods were being checked. The supplier's corrective-action plan named the affected lots, the suspected tooling wear and the date of the replacement tool. Cedar kept the severity split visible in its monthly report so that a cosmetic improvement could not hide a remaining safety-related defect. The invented figures show a method of working, not a typical result.
Watch out
Common mistakes.
- Comparing months without showing sample volume or product mix.
- Treating every defect as equally serious.
- Assuming more recorded rejects always means the supplier process worsened.
Questions
People also ask.
Is one high-defect lot a trend?
Not by itself, though a critical defect may still need immediate action.
Why show inspected units?
The denominator controls the rate and helps explain noisy small samples.
Can quality and on-time delivery be combined?
They can be reviewed together, but keep the underlying measures visible.
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