Make the decision path visible
A reference material can be stable, homogeneous and accurately assigned yet still behave unlike archaeological samples in a particular method. This guide shows how to test commutability, recognise matrix mismatch and restrict conclusions to the methods the evidence supports.
A reference material can be stable, homogeneous and accurately assigned yet still behave unlike archaeological samples in a particular method. This guide shows how to test commutability, recognise matrix mismatch and restrict conclusions to the methods the evidence supports. The aim is not to force certainty where the evidence is conditional. It is to show what can be used now, what needs further testing and what must remain visible to the next person.
The chapters move from first principles to a worked case, changed-context transfer, explicit limits, practical checks and an auditable decision. Start with the route closest to your task or read in sequence.
Choose the route closest to your decision
Chapter contents
Route 1: chapters 1–3
Route 2: chapters 4–6
Route 3: chapters 7–9
1. Define the measurand, material and method role
State what property is being measured, in which material, by which procedures and for what decision. Distinguish calibration, trueness control, method validation and proficiency use. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Is the reference material being asked to do the job for which its value and preparation were established? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. A certified soil supports elemental mass-fraction checks, but a laboratory also wants it to validate nondestructive portable X-ray fluorescence on weathered pottery. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the role test to collagen isotope work where extraction and matrix composition differ from a bulk organic control. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Certification does not make a material universal, and traceability of a value does not prove fitness for every field procedure. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Record certificate, measurand, property value, uncertainty, intended use, routine methods and the archaeological sample population. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
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2. Understand commutability as comparative behaviour
A material is commutable for stated procedures when it follows the same relationship across those procedures as authentic samples. The property belongs to a material–procedure combination, not to the bottle alone. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Do method differences for the reference material resemble method differences for real samples? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. Two digestion methods agree on the reference soil but diverge on high-carbonate archaeological sediments, showing that the material does not represent the relevant matrix effect. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the idea to spectroscopy by comparing spectral response relationships rather than only assigned concentrations. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Stable and homogeneous materials can be noncommutable, while a commutable material may still be unsuitable for another measurand. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Keep the procedures, sample types, comparison model, criterion and range over which the conclusion holds. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
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3. Describe the archaeological matrix
Characterise mineralogy, particle size, porosity, corrosion products, organic content, conservation treatment, burial alteration and expected interferences before selecting a reference. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Which matrix features can change extraction, atomisation, ionisation, fluorescence, adsorption or spectral response? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. A pressed geological powder lacks the glaze, porosity and layered weathering of ceramic sherds, so its response to surface X-ray fluorescence may differ. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the matrix map to bone where diagenesis and consolidants influence both preparation and signal. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Matching an analyte concentration does not make two matrices equivalent. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Record representative sample descriptors, preparation history, heterogeneity, known interferents and the mechanism by which each may affect the method. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
| Checkpoint | What to test |
|---|---|
| Decision question | Which matrix features can change extraction, atomisation, ionisation, fluorescence, adsorption or spectral response? |
| Worked comparison | A pressed geological powder lacks the glaze, porosity and layered weathering of ceramic sherds, so its response to surface X-ray fluorescence may differ. |
| Transfer test | Transfer the matrix map to bone where diagenesis and consolidants influence both preparation and signal. |
| Known boundary | Matching an analyte concentration does not make two matrices equivalent. |
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4. Choose representative samples and procedures
Select routine archaeological samples spanning the intended range and include every procedure for which commutability will be claimed. Prequalify method precision so noise does not masquerade as matrix mismatch. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Does the study represent the specimens, concentrations and procedures used in practice? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. The design includes fresh fracture, weathered surface and conserved ceramic samples across three instruments rather than a small set chosen for convenience. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the selection to metals by spanning alloy composition and corrosion state. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. A narrow sample panel can make a material look commutable only because difficult matrices were excluded. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Keep inclusion rules, sample count, range coverage, randomisation, replicate plan and reasons for excluding any procedure. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
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5. Set the criterion before seeing results
Define a difference-in-bias, prediction-interval or calibration-effectiveness criterion tied to the decision. State allowable uncertainty and how future use will be generalised. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Would a deviation at the criterion boundary change classification, provenance or conservation action? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. The team sets a maximum method-specific bias that would not change whether lead exceeds the interpretive threshold, then evaluates the reference material against it. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the criterion to isotope ratios where a much smaller bias may alter geographic interpretation. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Statistical significance is not a commutability criterion, and a wide acceptance band can conceal an unusable material. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Record the scientific requirement, criterion, confidence approach, multiple comparisons and the authority that approved the boundary. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
| Checkpoint | What to test |
|---|---|
| Decision question | Would a deviation at the criterion boundary change classification, provenance or conservation action? |
| Worked comparison | The team sets a maximum method-specific bias that would not change whether lead exceeds the interpretive threshold, then evaluates the reference material against it. |
| Transfer test | Transfer the criterion to isotope ratios where a much smaller bias may alter geographic interpretation. |
| Known boundary | Statistical significance is not a commutability criterion, and a wide acceptance band can conceal an unusable material. |
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6. Work a matrix-mismatch case
Compare routine samples and the reference across methods, inspect residuals and identify whether the reference sits outside the authentic-sample relationship. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Would the same correction that aligns real samples also align the reference material? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. Digestion ICP-MS and portable XRF track each other for archaeological soils, but the reference powder shows an unusually strong XRF response. The lab restricts it to digestion quality control. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Change the context to pressed pellets prepared identically to the reference and test whether commutability improves. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. A single outlying material may reveal matrix mismatch, contamination, preparation error or method nonlinearity; diagnose before naming the cause. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Save raw results, plots, model, residuals, uncertainty, preparation details, excluded runs and the bounded conclusion. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
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7. Separate noncommutability from other errors
Investigate calibration fit, assigned-value error, instability, inhomogeneity, carry-over and preparation differences before attributing disagreement to commutability. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Which mechanism predicts the observed pattern across samples and procedures? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. All specimens drift after a reagent change, indicating calibration or preparation failure; only the reference diverges after correction, supporting a matrix-specific explanation. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the diagnostic tree to microscopy counts where operator classification can replace instrumental calibration as the alternative cause. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Noncommutability is not a catch-all label for any failed comparison. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Retain control charts, lot information, stability evidence, homogeneity checks, blanks, calibration data and diagnostic decisions. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
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8. Quantify method-specific bias and uncertainty
Estimate the material-specific deviation for each relevant procedure and express whether it matters at the intended threshold. Include repeatability and model uncertainty. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Can the bias be distinguished from normal method variation, and is it stable across the range? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. A reference shows negligible bias for wavelength-dispersive XRF but a concentration-dependent positive bias for handheld XRF on rough surfaces. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the estimate to organic residue assays where recovery rather than instrument signal may drive the difference. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. A single average bias can hide concentration, mineralogy or preparation dependence. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Keep procedure-specific estimates, confidence intervals, range restrictions, influential samples and a rule for future verification. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
| Checkpoint | What to test |
|---|---|
| Decision question | Can the bias be distinguished from normal method variation, and is it stable across the range? |
| Worked comparison | A reference shows negligible bias for wavelength-dispersive XRF but a concentration-dependent positive bias for handheld XRF on rough surfaces. |
| Transfer test | Transfer the estimate to organic residue assays where recovery rather than instrument signal may drive the difference. |
| Known boundary | A single average bias can hide concentration, mineralogy or preparation dependence. |
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9. Decide whether to restrict, replace or supplement
A noncommutable material may still support a narrower task. State approved procedures and claims, or supplement it with matrix-matched controls and authentic-sample comparisons. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. What useful function remains without implying broader validity? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. The material remains suitable for digestion recovery and instrument stability but is removed from claims about nondestructive surface analysis. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the graded disposition to training, proficiency testing or qualitative identification. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Relabelling a material as a check sample must not hide the loss of traceable or trueness claims. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Record permitted uses, prohibited uses, replacement plan, labels, laboratory information-system status and authoriser. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
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10. Bridge methods, laboratories and lots cautiously
Repeat or bridge commutability evidence when methods, instruments, preparation, software, material lots or sample populations change. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Does the earlier conclusion cover the new procedure and archaeological matrix, or only share a familiar name? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. A new handheld XRF firmware changes spectral deconvolution, so the old commutability study is not assumed to transfer without comparison. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the bridge to a replacement reference lot using overlapping samples and unchanged decision criteria. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Agreement between old and new reference lots does not prove agreement with authentic samples. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Keep change assessment, overlap design, acceptance criteria, method versions and the date the conclusion expires or requires review. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
| Checkpoint | What to test |
|---|---|
| Decision question | Does the earlier conclusion cover the new procedure and archaeological matrix, or only share a familiar name? |
| Worked comparison | A new handheld XRF firmware changes spectral deconvolution, so the old commutability study is not assumed to transfer without comparison. |
| Transfer test | Transfer the bridge to a replacement reference lot using overlapping samples and unchanged decision criteria. |
| Known boundary | Agreement between old and new reference lots does not prove agreement with authentic samples. |
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11. Answer practical laboratory questions
Explain whether one CRM can validate every method, whether matching concentration is enough, how many samples are needed and what to do after a noncommutable result. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Can every answer identify the material–procedure scope and the evidence behind it? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. An analyst asks why a certified powder cannot validate surface XRF. The answer shows how surface state and matrix affect response despite a reliable assigned value. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the explanation to collaborators so reference-material claims remain consistent across reports. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Do not borrow clinical commutability thresholds unchanged; formal criteria must fit the archaeological measurand and decision. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Publish approved answers, escalation route, study requirements, review date and references to the certificate. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
Can one threshold settle every case?
No. A threshold belongs to a purpose, population, evidence base and consequence structure. Recheck it when any of those change.
Does more data always make the answer safer?
No. Repeated or poorly controlled data can reproduce the same blind spot and increase confidence without increasing validity.
When should an irreversible action pause?
Pause when a plausible unresolved condition could change the action and targeted evidence or a reversible alternative is proportionate to the risk.
What makes the process auditable?
Another person must be able to find the inputs, transformations, assumptions, alternatives, authority, decision and residual uncertainty without relying on memory.
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12. Audit the evidence across the material lifecycle
Link receipt, preparation, commutability study, method changes, uses and reported claims. Reassess affected results if a material is later restricted. In reference materials used to validate measurements of archaeological soils, ceramics, metals, residues and biological remains, the practical claim is whether the relationship between methods for the reference material reflects the relationship observed for real archaeological samples. The chapter therefore begins with the decision boundary: what the evidence must support, what it may suggest and what it cannot safely establish.
First-principles check. Can the laboratory identify every conclusion that relied on the questioned material–method relationship? Name the object being compared, the mechanism that could create error and the consequence of a wrong answer. Make the time window, population, method and authority explicit before accepting a score, label or workflow result.
Worked practice. A software update reveals an old matrix-specific correction was omitted; the lab rechecks reports where the reference had been used to validate handheld XRF. The important sequence is visible: observations come first, alternative explanations are tested, the bounded inference is stated and the action follows. This prevents the conclusion from becoming stronger merely because it is convenient.
Changed-context transfer. Transfer the audit to shared repositories by preserving method-specific qualification with the material record. Carry over the reasoning steps, not the old threshold. Replace the local data, controls, costs and consequences, then ask whether the same conclusion still holds. A copied answer is not transfer if a hidden assumption changed.
Limit and misconception. Retiring a material does not resolve historical overclaims. The recurring danger is that a well-characterised material is assumed to validate a routine method even though its matrix behaves differently. A careful analysis marks the boundary and keeps competing explanations available until evidence genuinely excludes them.
Evidence record. Keep the evidence package, impact assessment, corrective action, future trigger and verified specialist routes. Add source, date, operator or analyst, method and software version, exclusions and uncertainty. Preserve earlier states and link raw observations to derived decisions so that a later reviewer can challenge one step without losing the chain.
Decision-quality drill. Write one sentence naming the action supported now and one naming the strongest unsupported claim. Then change one plausible condition—threshold, method, missing record or stakeholder cost. If the action reverses, label the decision sensitive and set a review trigger.
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Continue through verified routes
Return to the core Gold Standard framework or continue into the specialist routes that directly extend this decision. The external sources below define or test the concepts used here.
Authoritative sources
- NIST SP 260-136: Metrological Tools for Reference Materials
- NIST: Recommendations for assessing commutability, Part 1
- NIST: Criterion for assessing commutability of secondary calibrators
- NIST: Commutability assessment of new SRMs for vitamin D
Guidance, methods and datasets can change. Recheck the linked source, local evidence and decision context before carrying the conclusion into a new case.