EI-201b · Module 2

Multi-Source Corroboration

3 min read

Corroboration is the process of verifying a signal across multiple independent sources before treating it as confirmed intelligence. The key word is independent — two articles citing the same original report provide zero corroboration. Two sources that independently observed the same event provide strong corroboration. The VANGUARD corroboration standard requires two independent sources for MEDIUM-confidence signals and three independent sources for HIGH-confidence signals. LOW-confidence signals can be reported from a single source with explicit caveats.

Do This

  • Verify source independence — do the two sources actually have independent access to the information, or are they both citing the same primary source?
  • Weight corroboration by source layer — a Layer 1 + Layer 3 corroboration (primary source + human source) is stronger than Layer 2 + Layer 2 (two aggregators)
  • Report the corroboration level in your briefing — "corroborated by 3 independent sources" is more useful than "confirmed"

Avoid This

  • Count re-reports as independent corroboration — ten articles citing the same press release is one source, not ten
  • Require corroboration for time-sensitive flash alerts — sometimes you must report from a single high-credibility source with appropriate caveats
  • Treat corroboration as binary — the number of sources, their credibility scores, and their independence all matter

There is a tension between corroboration and timeliness. The highest-value signals are often the ones that break first — before corroboration is possible. The VANGUARD protocol handles this by allowing single-source reporting for score-5 sources with a [SINGLE SOURCE] label. For score-3 or lower sources, single-source signals go into the horizon watch section as developing situations, not the main briefing as confirmed intelligence. This protocol preserves both speed and credibility.