---
title: "Source Reliability | Altss Glossary"
description: "Source reliability is an assessment of how dependable a source has proven to be, based on its record, access and conduct, graded separately from the…"
canonical: "https://altss.com/glossary/source-reliability"
---

Glossary · Evidence & data

# Source Reliability

Also called: source reliability grading

Source reliability is an assessment of how dependable a source has proven to be, based on its record, access and conduct, graded separately from the credibility of any single item of information it supplies.

Publisher: Altss LLCContent modified 2026-10-01

ALTSS-DATA-007

Two questions are asked about every piece of information: is the source usually right, and is this particular item believable? Intelligence practice answers them on two separate scales so that a usually reliable source's weak claim and an unknown source's well-confirmed claim are not confused. Reliability belongs to the source; credibility belongs to the item.

### Formal definition

The system of the North Atlantic Treaty Organization (NATO), set out in Allied Joint Publication AJP-2.1 and also called the Admiralty Code, grades source reliability from A (completely reliable) to E (unreliable), with F where reliability cannot be judged, and information credibility from 1 (confirmed by other sources) to 5 (improbable), with 6 where truth cannot be judged; the two are to be evaluated independently. The Berkeley Protocol uses reliability for the ability to perform consistently and dependably, credibility for believability, and veracity for conformity with fact.

## The Admiralty (NATO) grading system

The system was developed by the British Admiralty's Naval Intelligence Division during the Second World War and is used in NATO intelligence doctrine. Each item gets a letter and a number, for example "B2".

| Grade | Source reliability | Grade | Information credibility |
| --- | --- | --- | --- |

| A | Completely reliable | 1 | Confirmed by other sources |

| B | Usually reliable | 2 | Probably true |

| C | Fairly reliable | 3 | Possibly true |

| D | Not usually reliable | 4 | Doubtful |

| E | Unreliable | 5 | Improbable |

| F | Reliability cannot be judged | 6 | Truth cannot be judged |

The doctrine document itself is not publicly available; the labels above follow peer-reviewed reproductions. The two axes are meant to be independent: a reliable source can pass on an unconfirmed rumour (A3), and a source with no track record can supply something independently confirmed (F1).

## Reliability, credibility and veracity

- **Reliability** is a property of the source: how dependably it has reported in the past, for this kind of information.

- **Credibility** is a property of the item: whether it is confirmed by independent sources, consistent with what else is known, and plausible. Credibility grade 1 rests on [triangulation](https://altss.com/glossary/source-triangulation).

- **Veracity** is whether the item is in fact true, which neither grade establishes.

US intelligence analytic standards (ICD 203) list the factors that bear on source quality and credibility: accuracy and completeness, possible denial and deception, the age and continued currency of the information, technical elements of collection, and the source's access, validation, motivation, possible bias and expertise. The Berkeley Protocol adds, for [open sources](https://altss.com/glossary/osint) online, the source's posting history, its independence and affiliations, and how specific its claims are (paras. 177-181).

## Grading reliability in practice

Reliability is graded per kind of claim. A companies register is dependable for registration status and less so for a free-text business description its filers supply, which is self-reported data that registers commonly publish as supplied. A trade publication with its own reporting may be dependable for fund closes and weaker on allocation targets. A grade changes only for a recorded reason, such as errors found on recheck, a correction history, or a change in the source's practices. Reputation, size and brand are not reasons.

Reliability is also not the same as source authority. Authority is the standing of a class of source to state a type of claim (a registry for what it registers, a plan for its own votes). Reliability is the track record of a specific source. An authoritative source can still be graded down for repeated filing errors; a non-authoritative one can be reliable and still not settle the question.

## Known weaknesses of letter-number grading

Irwin and Mandel (2019) argue that such information evaluation methods mask rather than guide subjectivity, and propose flexible guidelines instead, including numeric probability estimates of how likely the information is to be accurate and periodic re-evaluation as new information arrives. Kelly and co-authors (2025) report that, despite the instruction to grade independently, raters often assign the two codes so that they line up, and that judgments of trustworthiness lean more on source reliability than on information credibility. The practical lessons: record the reason for each grade, re-grade when the record changes, and do not let a good source grade stand in for checking the item.

## How Altss applies this (Altss methodology)

Altss's [Source Reliability & Confidence Methodology](https://altss.com/knowledge-center/frameworks/source-reliability-and-confidence-methodology) adapts the two NATO axes: a reliability grade from A to F for each source per claim type and a credibility grade from 1 to 6 for each item, recorded separately from a third, Altss-defined judgement, the source's authority class. A single combined "source score" is not kept in their place.

Under Altss's three-dimension evidence model, reliability is a property of the source and is never used as a value of any evidence dimension. **Evidence origin** says what kind of source stated the claim (for example REGULATORY_PUBLIC_RECORD or OSINT_SOURCED); **derivation status** says whether the value was OBSERVED, DERIVED or ESTIMATED; **validation status** (UNVERIFIED, CORROBORATED, RESEARCH_VALIDATED or CONFLICTING, stated with a date) says what checking the claim has passed; **reliability** says how dependable that particular source has been. A filing's origin does not make its filer reliable, and a reliable source does not make a claim corroborated. No commercial relationship with a subject changes a source's grade.

## Not the same as

- [Triangulation (Source Triangulation)](https://altss.com/glossary/source-triangulation): Triangulation tests an item against independent sources and feeds its credibility grade; it says nothing about any one source's reliability.

- [Confidence Score](https://altss.com/glossary/confidence-score): A confidence score summarises support for a claim or judgment; source reliability is one input to it, not the score itself.

- [Primary Source](https://altss.com/glossary/primary-source): Primary describes how close a source is to the fact; reliability describes how dependable the source has proven to be. A primary source can be unreliable, and a secondary one reliable.

## Common mistakes

- Merging reliability and credibility into one score, so that a reliable source's unconfirmed claim reads as confirmed.

- Grading a source by reputation or size rather than by its record for the claim type in question.

- Treating F (reliability cannot be judged) as if it were E (unreliable), or as an average grade.

- Grading a source once for every kind of claim it makes.

- Treating a source category, such as "regulatory filing", as a reliability grade.

- Never re-grading a source after its errors or corrections are found.

## Edge cases

- A new publication with no track record is graded F, not penalised as unreliable.

- A reliable outlet quoting an unnamed person: the outlet's reliability does not transfer to its anonymous source, and the item's credibility depends on confirmation.

- A source that changes ownership or editorial practice is re-graded with the reason recorded; older items keep the grade that applied when they were published.

- A registry can be graded highly for its own determinations (registration status, identifiers) and lower for content its filers type in.

## Questions

### What does a grade like "B2" mean?

In the Admiralty (NATO) system, B means the source is usually reliable and 2 means the information is probably true. The letter grades the source; the number grades the item.

### Can an unreliable source supply true information?

Yes. That is why credibility is graded separately: an item from a source graded D or F can still be confirmed by independent sources.

## External standards

| Standard | Relation | Note |
| --- | --- | --- |

| NATO AJP-2.1 (Admiralty Code) (Source reliability A-F; information credibility 1-6) | equivalent | Doctrine not public; labels per peer-reviewed reproduction (Table 1). |

| ICD 203 Analytic Standards (US) (Tradecraft standard D.6.e(1)) | related |  |

## Sources

- [The effect of source reliability and information credibility on judgments of information quality in intelligence analysis](https://doi.org/10.1017/jdm.2025.10007). Megan O. Kelly; David V. Budescu; Mandeep K. Dhami; David R. Mandel, Judgment and Decision Making (Cambridge University Press), Vol. 20, e36 (2025); open access, CC BY. Status: Published (checked 2026-10-01). Table 1; Introduction — supports: Scale labels, origin of the Admiralty Code, requirement to grade the two axes independently, and evidence that raters align them

- [Improving information evaluation for intelligence production](https://doi.org/10.1080/02684527.2019.1569343). Daniel Irwin; David R. Mandel, Intelligence and National Security, Vol. 34(4), pp. 503-525. Status: Published (paywalled) (checked 2026-10-01). Abstract; Vol. 34(4), pp. 503-525 — supports: Information evaluation methods mask rather than guide subjectivity; proposes numeric probability estimates of information accuracy and periodic re-evaluation

- [Intelligence Community Directive 203: Analytic Standards](https://archive.dni.gov/files/documents/ICD/ICD-203.pdf). Office of the Director of National Intelligence, ODNI, Signed 2 January 2015; technical amendments incl. 21 January 2022. Status: In force (as amended) (checked 2026-10-01). Section D.6.e(1) — supports: Factors affecting source quality and credibility

- [Berkeley Protocol on Digital Open Source Investigations](https://humanrights.berkeley.edu/publications/berkeley-protocol-on-digital-open-source-investigations/). OHCHR; Human Rights Center, UC Berkeley School of Law, United Nations (OHCHR) and UC Berkeley, HR/PUB/20/2; launched 2 December 2020; printed edition (c) 2022 United Nations. Status: Current (checked 2026-10-01). Para. 23 (credibility, reliability, veracity); paras. 177-181 (source analysis) — supports: Definitions of reliability and credibility; source analysis factors for online sources

## Related terms

5 terms

- [Triangulation (Source Triangulation)](https://altss.com/glossary/source-triangulation)

- [Confidence Score](https://altss.com/glossary/confidence-score)

- [Primary Source](https://altss.com/glossary/primary-source)

- [Open-Source Intelligence](https://altss.com/glossary/osint)

- [Data Provenance](https://altss.com/glossary/data-provenance)

## Referenced by

1 term

- [Data Quality Dimensions](https://altss.com/glossary/data-quality-dimensions)

## Concept record

Concept ID

ALTSS-DATA-007

Classification

Evidence & data

Topics

Private markets data & OSINT

Version

2.0.0

Last reviewed

2026-10-01

Structured data

[JSON](https://altss.com/reference/concepts/source-reliability.json)

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