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Stagewise Availability Assay

Diagnostic assay — instantiates Effective-Input Delivery Assurance

Measures how much of the input remains in usable form at each stage of the path, turning one supplied figure into a stagewise availability profile with error bars.

A measurement technique that samples the input at each stage of the delivery path and assays how much usable material is actually present there, converting a single "amount supplied" into a stage-by-stage availability profile — each point carrying its own measurement uncertainty. Its defining move is being the instrument step that generates the raw per-stage numbers everything else consumes: it does not aggregate them into a ratio, explain the drop, or define the target — it produces trustworthy measurements, with error bars, at each checkpoint. Its whole value is replacing an assumption ("we added X") with a measurement ("Y ± e is actually here, now").

Example

An iodized-salt fortification program iodizes salt at the plant to ≈40 ppm — comfortably above the population requirement on paper. But iodine is volatile; it sublimes with heat, humidity, and time. The Stagewise Availability Assay measures iodine content at each stage of the path: at the factory (≈40 ppm), after warehouse storage (≈34 ppm), at rural retail following transport in jute sacks (≈28 ppm), in the household after weeks in an open container near a stove (≈22 ppm), and — critically — after cooking, since iodine is lost when salt is added early to boiling food (≈16 ppm actually ingested). Each reading is a titration or spectrometric assay reported with an uncertainty band (about ±3 ppm).

The profile shows the nominal 40 ppm is roughly 16 ppm by the point of action — a loss curve completely invisible if you test only at the plant. The assay produced the numbers and their error bars; whether 16 ppm is "enough" is a judgment left to another mechanism.

How it works

  • Sample and assay at each stage checkpoint. Draw a representative sample and measure usable content — the active/usable form against a defined criterion — not mere presence.
  • Report each stage as a value with an uncertainty band, never a bare point, so how well each stage is known travels with the number.
  • Hold the method constant across stages so the drop between stages is real loss, not method drift — the single most important condition for a comparable profile.

Tuning parameters

  • Assay sensitivity / specificity — how finely it distinguishes usable from degraded form; higher specificity avoids counting inactive residue but costs more per reading.
  • Sampling plan — how many samples per stage and how representative; sparse sampling widens the uncertainty band.
  • Stage resolution — how many checkpoints along the path; more stages localize the loss but multiply cost.
  • Uncertainty treatment — report a band, a full distribution, or a point, and how conservatively the band is set.
  • Method consistency — one assay across all stages versus stage-appropriate methods; mixing methods risks confounding real loss with method difference.

When it helps, and when it misleads

Its strength is replacing the fiction that supplied equals available with measured reality at each stage, and its error bars keep everyone honest about how much is genuinely known versus assumed.

An assay measures only what its method captures: if it counts total content rather than the usable form, it overstates availability — measuring the iodine that is present rather than the iodine actually absorbable and utilized, the bioaccessibility-versus-bioavailability gap.[1] Its classic misuse is to sample the convenient stage (the factory) and report it as the point-of-action value. The discipline that keeps it honest is to assay against a usable-form criterion, carry the uncertainty band forward instead of collapsing it, and measure as close to the point of action as the method allows rather than at the easiest checkpoint.

How it implements the components

Stagewise Availability Assay fills the measurement side of the archetype — and only that:

  • stagewise_availability_measurement — its core output: the measured usable amount at each stage of the path.
  • uncertainty_band — every reading carries a measurement uncertainty band, so the profile states how well each stage is known.

It does not define what "usable form" means or validate a target proxy (that is Target-Site Sampling or Proxy Validation), aggregate the readings into an availability ratio or watch them over time (Availability Funnel Dashboard), or attribute the loss between stages (First-Pass Loss Audit); this mechanism measures, it does not judge, display, or explain.

References

[1] In nutrition science, bioaccessibility (the fraction released from its matrix and available for absorption) is distinct from bioavailability (the fraction actually absorbed and utilized). An assay that measures total or bioaccessible content can overstate what reaches the point of action when the usable, bioavailable fraction is smaller. ↩