Aggregate vector
Per-result classification tells the agent about each source. The aggregate vector tells the agent about the SERP as a whole — whether the landscape is diverse, vendor-dominated, authoritative, or structurally commercial.
Schema
Section titled “Schema”interface AggregateVector { tier_distribution: Record<Tier, number>; // count per tier, full SERP (not the trimmed max_results) mean_editorial_standards: "high" | "medium" | "low" | "unknown"; mean_authoritative_weight: number; // 0..1, arithmetic mean over results diversity_entropy: number; // Shannon entropy of tier_distribution vendor_dominance_ratio: number; // (vendor_primary + vendor_content_marketing) / total}The four metrics in practice
Section titled “The four metrics in practice”tier_distribution
Section titled “tier_distribution”Raw counts per tier. The agent can inspect this directly — “3 peer_reviewed, 7 vendor_content_marketing” communicates more than a summary score can.
mean_authoritative_weight
Section titled “mean_authoritative_weight”The SERP’s overall trust level as a single scalar. Empirical observations across the 5-layer probe suite:
| Layer | Query style | mean_auth |
|---|---|---|
| A (regulated) | GDPR Article 17 right to erasure scope | ~0.70 |
| B (academic phrasing) | transformational leadership meta-analysis effect size | ~0.87 |
| B (general phrasing) | what makes a good leader | ~0.38 |
| C (SaaS operational) | series B saas magic number benchmark | ~0.23 |
Below ~0.3, an agent should treat aggregated claims as commercial positioning, not research.
diversity_entropy
Section titled “diversity_entropy”Shannon entropy of the tier distribution. Low entropy = the SERP is dominated by a single tier. High entropy = the SERP spans many tiers.
Important: low entropy is not automatically bad. A SERP of 10/10 peer-reviewed papers has entropy 0.0 and that’s a feature. sift’s summary_hints suppress the “low diversity” warning when mean_authoritative_weight >= 0.7 precisely for this reason.
vendor_dominance_ratio
Section titled “vendor_dominance_ratio”Fraction of results classified as vendor_primary or vendor_content_marketing. Not the same as “commercial ratio” — affiliate results aren’t counted here. See Summary hints for the hints that fire at 50%+ and at 90%+ without non-commercial alternatives.
Aggregate is over the full SERP, not the trimmed output
Section titled “Aggregate is over the full SERP, not the trimmed output”When max_results=5 is passed but sift fetched 10, the aggregate is computed over all 10. The agent should see the real landscape even when it asked for a smaller trimmed view. This is deliberate: aggregate metrics for too few results are noisy and misleading.