The Lab Says “Not Detected”. Does That Mean Zero?

A Favourable Result With an Important Limit

A manufacturer is developing a lower-temperature curing process for a protective polymer coating.

The research team wants to determine whether the revised process can reduce residual processing chemicals while maintaining the coating's required mechanical properties.

Experimental specimens are prepared using the proposed method and submitted for chemical analysis.

The laboratory report states that the target residual compound was not detected.

The result appears encouraging.

The engineering team interprets it as evidence that the revised process has eliminated the compound.

But the laboratory result may support a narrower conclusion.

The distinction matters if the technical question is whether the process has reduced the residual compound below a particular level.

If the analytical method cannot reliably distinguish concentrations around that level, the experiment may not establish whether the intended outcome has been achieved.

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality distinguish a substance that is not detectable by a specified analytical method from one that is necessarily absent. Their guidance also treats observations below analytical detection limits as censored observations rather than automatically assigning them a concentration of zero. Australian and New Zealand Guidelines — Glossary of Terms

Although that guidance concerns environmental measurements, the analytical distinction is relevant to other experimental investigations involving chemical concentrations.

A laboratory can therefore report a technically valid result while the result remains insufficient to answer the research question.

The problem is not necessarily laboratory performance.

Start With the Concentration the Experiment Needs to Resolve

The analytical method should be selected around the technical question.

Before testing begins, the research team should understand what concentration range matters to the decision.

Consider two different questions.

These questions require different evidence.

To demonstrate a reduction, the analytical method needs to distinguish the relevant concentrations across the experimental conditions.

To determine whether a defined level has been reached, the method needs adequate performance around that level.

The Australian and New Zealand water-quality guidance recommends confirming before analysis that the selected method covers the expected concentration range, can detect the minimum concentration of interest and provides sufficient accuracy and precision. Australian and New Zealand Guidelines — Laboratory Analysis

If the laboratory's applicable reporting limit is above the concentration relevant to the decision, a non-detect result may leave the central question unresolved.

Conversely, if the applicable method limit is sufficiently below the technical threshold and the method is otherwise appropriate for the sample, the non-detect result may provide enough evidence for that particular decision.

Understand What the Laboratory Means by “Not Detected”

Analytical reports may use terms such as:

These terms should not automatically be treated as interchangeable.

Laboratories and analytical methods may define and apply their limits differently.

A detection limit generally relates to the lowest concentration at which the presence of an analyte can be distinguished under specified analytical conditions.

A reporting or quantification limit may instead reflect the level above which the laboratory is prepared to provide a quantitative result meeting its stated analytical requirements.

The important step is therefore to understand the definition used in the particular laboratory report.

The National Measurement Institute, for example, publishes method-specific limits of reporting for environmental analyses, including different reporting limits for particular hydrocarbon fractions and sample types. National Measurement Institute — Total Recoverable Hydrocarbons

This illustrates an important point:

A business should therefore avoid treating “not detected” as a complete technical conclusion without understanding the method behind that statement.

Consider Whether the Sample Changes the Method's Performance

Analytical sensitivity can also depend on the sample itself.

A method that performs adequately with a reference material or familiar sample may encounter additional interference when applied to a new experimental material.

In the coating example, components of the new polymer formulation might affect extraction, recovery or analytical detection of the residual compound.

The research team should therefore establish whether the selected method is suitable for the relevant sample matrix.

Depending on the analytical method, quality-control evidence may include blanks, reference materials, replicate analyses or recovery checks.

The Australian and New Zealand laboratory guidance identifies quality-control procedures as important for assessing analytical performance and identifying potential problems affecting the reliability of results. Australian and New Zealand Guidelines — Laboratory Analysis

The objective is not to create an unnecessarily complicated laboratory programme.

Preserve the Result the Laboratory Actually Reported

Non-detect observations should remain identifiable in the research record.

They should not silently become ordinary numerical measurements.

Suppose five specimens from the revised curing process are all reported below the same analytical limit.

Entering those results as zero would imply that the compound was absent from every specimen.

Similarly, automatically replacing every non-detect result with half the reporting or detection limit introduces estimated values that were not directly measured.

Such substitution methods may have uses in particular analytical contexts, but they are not neutral.

Australian and New Zealand guidance on censored water-quality data explains that simple substitution methods can distort statistical estimates, particularly where a substantial proportion of observations falls below detection limits. It recommends retaining information about censored observations and selecting an analytical approach appropriate to the dataset. Australian and New Zealand Guidelines — Data Preparation and Exploration

For an engineering research project, the basic principle is simpler:

If the laboratory reported a result below a specified analytical limit, the project database should retain that status and the relevant limit.

The research team can then determine how the result should be treated for the particular analysis.

Two Non-Detects Do Not Necessarily Show Which Process Is Better

Consider an experiment comparing the existing curing process with the proposed lower-temperature process.

Suppose both groups are reported below the same analytical limit.

That finding may be useful.

It may establish that both processes produced concentrations below the method's reporting capability.

But it does not necessarily establish that the revised process leaves less residual compound.

That distinction is important if the research hypothesis concerns improvement rather than merely remaining below a defined threshold.

A more sensitive analytical method may be needed if distinguishing those concentrations is important to the decision.

However, more sensitive testing is not automatically necessary.

If the company's technical question is simply whether the concentration is below a specified level, and the existing analytical method can adequately establish that, further analytical precision may add little value.

Keep Measurement Limitations Separate From R&DTI Eligibility

A measurement problem does not automatically create an R&D activity.

Selecting a more sensitive laboratory method, correcting a known analytical problem or applying an established analytical technique may simply be routine technical work.

There is also a specific R&DTI exclusion for activities associated with complying with statutory requirements or standards. That exclusion includes routine testing and analysis of materials, components, products, processes and other things when the activities are associated with meeting those statutory requirements or standards. Australian Government — Excluded R&D Activities

This does not mean that every routine laboratory analysis is automatically covered by that statutory exclusion.

Nor does the use of a sophisticated analytical method establish core R&D.

A different situation may arise where the experimental material itself presents an outcome that existing knowledge cannot determine.

For example, researchers may be investigating whether an unfamiliar interaction between polymer formulation and curing conditions changes the formation or retention of a residual compound.

The analytical method would then provide evidence for testing that technical hypothesis.

Under the current R&DTI requirements, a core R&D activity must be conducted for the purpose of generating new knowledge.

Its outcome must be unable to be known or determined in advance by a competent professional on the basis of current knowledge, information or experience.

The outcome must then be determined through a systematic progression of work based on principles of established science, proceeding through hypothesis, experiment, observation and evaluation and leading to logical conclusions. Australian Government — Conducting Core R&D Activities

Preserve the Measurement Limitation in the Research Record

Current Australian Government R&DTI guidance states that records should be created at the time the activity is conducted.

Records should show relevant background research and what was done, how the work was performed, when it occurred and who carried it out. Australian Government — Record Keeping for the R&D Tax Incentive

For an experiment involving analytical limits, a practical technical record may also preserve:

The purpose is to prevent a later project report from turning:

into:

For engineering leaders, that distinction determines whether the proposed technology has actually demonstrated the intended behaviour.

For CFOs, it helps distinguish additional research expenditure that could resolve a material uncertainty from routine analytical work that would not change the decision.

Conclusion

“Not detected” does not mean “not present”.

It means the analytical method did not produce a reportable detection under the conditions and criteria applied.

Whether that is sufficient depends on the technical question.

A non-detect may be entirely adequate evidence when the method can demonstrate performance below the level that matters.

It may be insufficient when the experiment needs to distinguish between concentrations below that analytical limit.

The useful question is therefore not:

It is:

A non-detect result can be valuable evidence.

It should simply not support a stronger conclusion than the measurement can justify.

Sources & Further Reading

• Australian and New Zealand Guidelines — Laboratory Analysis

• Australian and New Zealand Guidelines — Data Preparation and Exploration

• Australian and New Zealand Guidelines — Glossary of Terms

• National Measurement Institute — Total Recoverable Hydrocarbons

• Australian Government — Conducting Core R&D Activities

• Australian Government — Excluded R&D Activities

• Australian Government — Record Keeping for the R&D Tax Incentive