SUMMARY: Decision half-life is the period during which a conclusion remains reliable before changing evidence, conditions, or assumptions require a new review.
Decisions often outlive the situations that justified them. A risk label created during an unusual event becomes a permanent account attribute. A staffing rule designed for one traffic pattern survives a platform migration. A source assessed as reliable is quoted years later, after its access, incentives, and methods have changed.
The record may be historically accurate and operationally stale at the same time. Decision half-life separates those states. It asks how long a conclusion can be reused before its supporting conditions need to be observed again.
What Shortens the Half-Life
Volatility: conclusions about fast-changing systems decay sooner than conclusions about stable physical constraints.
Distance: every transformation between the original observation and the final decision introduces assumptions that can age independently.
Consequence: a low-cost recommendation can tolerate more uncertainty than a decision that limits access, movement, income, or appeal.
Feedback: a decision that changes the environment may invalidate the evidence used to make it. Enforcement can suppress the behavior a model expects to observe, making apparent success difficult to distinguish from missing visibility.
Attach a Review Clock
A durable record should include more than a creation date. Record the conditions that would shorten its useful life: a new data source, a policy change, a material dispute, an altered collection method, or a threshold crossing. Review should be triggered by those events even when the nominal expiration date has not arrived.
Data lineage identifies the transformations a record has inherited. Source expiry marks when an input should stop carrying current authority. Decision half-life applies both ideas to the conclusion built from those inputs.
Field assessment: a decision without a review clock quietly converts past evidence into permanent authority.
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