# Repeatability and reproducibility in WPC laboratories

Canonical: https://woodplasticcomposite.net/guides/repeatability-and-reproducibility-in-wpc-laboratories/
Language: en
Updated: 2026-10-15
Version: 1
Review: AI-assisted English editorial draft. Human technical review has not been recorded.

## Summary

Repeated testing by one operator and testing across operators or laboratories address different sources of variation. WPC development benefits from distinguishing them before ranking small performance differences.

## Technical context

A narrow spread within one test series does not establish that another laboratory will obtain the same result. Preparation, conditioning and equipment interpretation can introduce differences even when the nominal method name is identical.

https://woodplasticcomposite.net/guides/repeatability-and-reproducibility-in-wpc-laboratories/#technical-context

## What to measure and document

Use a planned comparison with traceable specimens and agreed procedures. Examine the measurement system before concluding that a small formulation change caused a real improvement. Retain individual results and observations instead of circulating averages alone.

https://woodplasticcomposite.net/guides/repeatability-and-reproducibility-in-wpc-laboratories/#verification-plan

## Implications for development and specification

When comparing supplier reports, check compatibility of methods and specimen states. If a decision turns on a small difference, request a controlled comparison. Laboratory precision is valuable, but it should not be confused with proof of a large practical advantage.

https://woodplasticcomposite.net/guides/repeatability-and-reproducibility-in-wpc-laboratories/#practical-decision

## Related reading and evidence limits

Official guidance on controlling measurement processes and supporting uncertainty statements. Use the linked work as related reading. The practical checks above are editorial recommendations, not reported test results or a substitute for product qualification.

https://woodplasticcomposite.net/guides/repeatability-and-reproducibility-in-wpc-laboratories/#reading-scope

## Key points

A narrow spread within one test series does not establish that another laboratory will obtain the same result.
Use a planned comparison with traceable specimens and agreed procedures.
When comparing supplier reports, check compatibility of methods and specimen states.

## Comparison

Review step | Evidence to retain
Material and geometry | Exact specimen or product identity
Verification | Method, conditions and individual observations
Decision | Approved scope and documented limitations

## What evidence is needed for repeatability and reproducibility in WPC laboratories?

Use a planned comparison with traceable specimens and agreed procedures. Examine the measurement system before concluding that a small formulation change caused a real improvement. Retain individual results and observations instead of circulating averages alone.

## Sources

1. NIST: statistical control of measurement processes — https://www.itl.nist.gov/div898/handbook/mpc/section2/mpc2.htm