How to Compare Coatings When One Test Panel Is Lost

A lost test panel creates a missing observation, not a convenient opportunity to improve the dataset. How the loss happened determines whether the remaining comparison is still credible. Document it before recalculating averages or preparing a presentation.

Classify the missing result

Distinguish accidental breakage, an identification error, an unreadable measurement and a product-related failure. If a coating became too hazy to measure by the planned optical method, removing that panel as “invalid” can erase the very failure the study was meant to detect. Record the appearance outcome even when a numerical result is unavailable.

Situation	Appropriate record
Panel dropped during unrelated handling	Time, cause and last valid result
Sample identity lost	Identity uncertain; do not assign by appearance
Product prevents planned measurement	Failure observation and measurement limitation
Instrument malfunction	Affected readings, verification and recovery plan

Respect the original comparison structure

In a paired design, each A panel may have a matched B panel from the same substrate group. Losing one member affects that pair. Do not silently pair the remaining panel with a convenient sample from another day. Show complete pairs separately and explain any additional analysis using unmatched observations.

For illustration, a trial starts with six matched pairs and ends with five complete pairs plus one unmatched B panel. Report both counts. Presenting twelve planned panels as twelve completed tests would be inaccurate, even if the laboratory performed twelve application steps.

Decide whether replacement is meaningful

A replacement made later may have a different cure age, operator or exposure history. It can provide supporting information, but it does not automatically recreate the original trial. Where feasible, repeat the whole affected block and label it as a separate run.

Set exclusion rules before the next trial, including who approves them and how reasons are preserved. Review whether the conclusion changes under reasonable interpretations of the missing result. If it does, the correct next step is more evidence, not a more confident headline.

Related guides

• Planning a Real-World Field Trial for Ceramic Coatings
• A Ceramic Coating Test with One Excellent Panel and One Poor Panel
• A Practical Minimum Difference for Ceramic Coating Comparisons

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