Continuous Surveillance

The Living Prior

A prior that is not updated is a prior that is ageing. Continuous surveillance is the mechanism that keeps L₀(t+1) current — so the next brief starts from an honest state of knowledge, not a stale one.

From periodic review to living prior

Level II Session 5 introduced the surveillance system as a tool for keeping a specific brief current. Session 3 of Level 5 reframes it: surveillance is not a brief-maintenance activity. It is the continuous process of updating the team's prior state — keeping θ′ honest between briefs, so that when the next policy question arrives, the starting point is as current as possible rather than months or years out of date.

The key shift is from event-driven surveillance (watching for updates to a specific finding) to state-driven surveillance (maintaining the team's overall evidence state as a living document). The difference is the difference between watching a single stock and managing a portfolio.

The living prior update — what triggers θ′ → θ′′

Five categories of signal should trigger an update to the team's prior state — not just to a specific brief, but to the shared prior library that all future briefs draw from:

HTAIn new assessment

Any new HTAIn publication supersedes extrapolated LMIC evidence in the prior library for its topic area. Update the prior library immediately. Note which existing briefs cited extrapolated evidence that is now superseded.

NHA annual release

New NHA data updates the OOP baseline across all active briefs. The prior library's baseline financial protection figures must be refreshed. Trigger: NHA release date, annually.

ε gap closed

A new peer-reviewed study or government report fills a named evidence gap from the prior library. The gap entry should be updated from "absent" to "emerging" or "available," and the anchor constraint should be reassessed. This is the highest-value signal — it directly reduces the error term.

Anchor case signal

A documented real-world case that matches an anchor population — a claim rejection, a catastrophic expenditure report, a community health worker account — enters the evidence base. These are λ updates: they sharpen the constraint and may strengthen or challenge existing recommendations.

Recommendation challenged

A Ministry counterpart, a donor, or a peer reviewer challenges a brief's recommendation with new evidence or a methodological objection. The challenge is a gradient signal — it tells you which direction the prior needs to move. Log the challenge and the response. Both are prior updates.

🎯 Key takeaway

Surveillance at Level 5 is not brief maintenance — it is prior maintenance. Five signals trigger a prior library update: new HTAIn assessments, NHA data releases, ε gaps being closed, anchor case signals, and recommendation challenges. Each one moves θ′ toward a more accurate representation of what is known. A team whose prior library is current is a team that starts every brief from a position of advantage. Session 4 takes this further: the federated evidence twin is what happens when this prior maintenance system is formalised at institutional scale.