17.1 Purpose
The uncertainty factor exists so that a determination distinguishes between a cost that is known and large and a cost that is assumed and large. Assurance sized without that distinction charges the diligent applicant and the undiligent applicant the same amount, and therefore purchases no diligence.
17.2 Evidence classes
Each input to a determination shall be assigned exactly one evidence class, reflecting the strength of the artifact the input is drawn from and the independence of its author.
| Class | Basis of the input | Author independence |
|---|---|---|
| E1 | Executed instrument, tariff or statute | Binding on a third party |
| E2 | Independent professional study, reviewed | Independent of the applicant |
| E3 | Professional study, unreviewed | Retained by the applicant |
| E4 | Applicant attestation or internal estimate | None |
| E5 | Assumption, analogue, or an input whose bound artifact has been amended or withdrawn | None |
17.3 Assignment rules
An input shall be bound to the artifact it is drawn from by cryptographic digest, together with the located span relied upon. An input that cites no stored artifact shall not be assigned a class above E5.
Class shall be assignable from the document type. An assessor shall not assign E1, E2 or E3 on the basis of an automated reading alone; such a class may be proposed but shall be confirmed by the accredited assessor of record before it enters the determination.
The second rule is the boundary between what a machine settles and what a person answers for. Digest comparison, recomputation and completeness are machine-settleable and are settled that way. The judgment that a particular study was genuinely independent is not, and is therefore reserved.
17.4 Uncertainty factor
The uncertainty factor for a bucket shall be computed as a linear function of the evidence credit of the class assigned:
c evidence credit of the assigned class — Part B
k uncertainty coefficient — Part B
The factor is bounded below at unity: better-than-required evidence removes uncertainty loading but shall not create a credit against the attributed cost. Credit for protection is granted under §13 and shall not be granted a second time here.
17.5 Re-verification
Where a bound artifact is amended, withdrawn, or fails digest comparison at any subsequent verification, every input bound to it shall be demoted to E5 and the determination of record shall be marked stale until recomputed.