How Reddit Citations Changed in Microsoft Copilot for High-Stakes Health and Medical Consumer Decisions

LLM Authority Index Research | High-Stakes Consumer Decisions | Health and Medical | Microsoft Copilot | July-September 2026

Reddit was not captured as a direct citation source in the strict matched Microsoft Copilot health and medical panel at either the July or September 2026 endpoint.

Across 135 exact prompt-plus-Copilot scenarios observed at both endpoints, 0 scenarios cited Reddit in both months, 0 lost Reddit, 0 gained Reddit and all 135 cited Reddit in neither July nor September.

Matched Reddit response coverage was therefore 0.00% in July and 0.00% in September.

Because there are no discordant matched pairs, there is no meaningful McNemar loss-versus-gain significance test to run. The correct result is not applicable.

This is not a 100% decline. There was no measured July Reddit baseline to lose.

The result is best described as platform-specific Reddit non-detection in this defined Copilot health corpus.

That non-detection occurred inside a very large and active citation market.

Across the broader three-month Microsoft Copilot health source study, the platform produced 1,511 eligible deduplicated responses, 6,114 substantive public-facing citation events, 1,335 registrable cited domains and 4,851 domain-response appearances after Copilot-specific infrastructure filtering.

Forbes ranked #1 at 10.32% response citation coverage, followed by Healthline at 8.80%, NCOA.org at 7.54%, GoodRx at 5.69%, and Google.com at 5.16%.

Reddit does not appear in the published Copilot health Top 100.

The #100 domain in that ranking appeared in 9 responses, equal to 0.60% response coverage.

The defensible conclusion is therefore narrow but commercially important:

In this frozen high-stakes health and medical Copilot corpus, Reddit was not detected in the matched July or September endpoints and did not reach the published three-month Top 100. That is a measured source-market result, not proof that Microsoft Copilot never cites Reddit.

Important: The parent Health and Medical Reddit study publishes Copilot-specific matched counts and matched response coverage, but it does not publish a separate Copilot-wide balanced July-to-September aggregate citation-event share or response-coverage table. This article therefore does not invent a Copilot aggregate endpoint percentage. It uses the verified 135-scenario matched panel for longitudinal endpoint analysis and the verified three-month Copilot source study for market context.

Answer Capsule

How did Reddit citations change in Microsoft Copilot for high-stakes health and medical decisions from July to September 2026? No measurable change was observed because Reddit was absent from the strict matched panel at both endpoints. Across 135 exact prompt-plus-Copilot scenarios, Reddit recorded 0 losses, 0 gains and 0 persistent citations, with matched coverage at 0.00% in both July and September. Reddit also did not reach the published three-month Copilot health Top 100. The correct interpretation is non-detection in this defined Copilot health corpus, not a percentage decline and not evidence that Microsoft Copilot never cites Reddit.

Key Findings

• The strict matched Copilot health panel contained 135 exact prompt-plus-platform scenarios.
• Reddit recorded 0 matched losses and 0 gains.
• There were 0 persistent Reddit citations.
• All 135 matched scenarios cited Reddit in neither endpoint month.
• Matched Reddit response coverage was 0.00% in July and 0.00% in September.
• Relative change is not applicable.
• McNemar testing is not applicable because there are no discordant pairs.
• Across the full three-month Copilot health source market, there were 1,511 eligible deduplicated responses.
• The cleaned source market contained 6,114 substantive public-facing citation events.
• Copilot cited 1,335 registrable domains in the health source market.
• The source study counted 4,851 domain-response appearances.
• Reddit did not appear in the published Copilot health Top 100.
• The #100 domain appeared in 9 responses, equal to 0.60% response coverage.
• Forbes ranked #1 at 10.32%, followed by Healthline 8.80%, NCOA.org 7.54%, GoodRx 5.69%, and Google.com 5.16%.
• The public source ranking excluded 1,300 Bing/OpenStreetMap technical and navigational entries.
• The excluded technical layer included 1,105 bing.com, 181 bing.net, 12 bingapis.com, and 2 openstreetmap.org entries.
• Only 35 of the health Top 100 domains also appeared in Copilot's broader High-Stakes Consumer Decisions Top 100.
• Only 40 domains stayed in the monthly Copilot health Top 100 in all three months.
• Copilot's health Top 100 had only 19.8% Jaccard similarity with Gemini's health Top 100 and 19.0% with ChatGPT's health Top 100.
• Copilot was the only measured health platform with no matched Reddit baseline at either endpoint.

Questions This Study Answers

• Was Reddit a measurable direct citation source in Microsoft Copilot for these high-stakes health decisions?
• Did same-prompt matched testing identify any Reddit gains or losses between July and September?
• Does zero measured Reddit visibility mean Microsoft Copilot never cites Reddit?

Why This Research Belongs in Daily AI Search Marketing Decisions

Article 66 isolates one source, Reddit, inside one platform, Microsoft Copilot, and one commercial decision family, Health and Medical. Its operating value comes from showing how to interpret repeated non-detection without confusing it with a percentage decline or a universal rule about Copilot.

1. Was Reddit directly cited at either matched Copilot Health endpoint?
2. Did the full three-month source study show Reddit as a material Copilot Health source?
3. What should marketers do when a source is not detected but the surrounding citation market is large and active?

The strict matched panel is unambiguous. Across 135 exact prompt-plus-Copilot scenarios, Reddit produced 0 persistent citations, 0 losses, 0 gains and 135 neither-month scenarios. Matched response coverage was 0.00% in July and 0.00% in September.

There are no discordant pairs, so a McNemar loss-versus-gain p-value is not applicable. A 100% decline would also be incorrect because there was no measured July Reddit baseline to lose.

Article 66 does not publish a separate Copilot-specific balanced aggregate July-to-September citation-event share or response-coverage percentage because the frozen parent Health study does not publish those values. The longitudinal claim is therefore based on the matched panel, not an invented aggregate percentage.

The three-month Microsoft Copilot Health and Medical source study adds quarter-wide context. It contains 1,511 eligible deduplicated responses, 6,114 substantive public-facing citation events, 1,335 registrable cited domains and 4,851 domain-response appearances after platform-specific infrastructure filtering.

Reddit did not reach the published Copilot Health Top 100. The #100 domain appeared in 9 responses, equal to 0.60% response citation coverage. That proves Reddit was below the frozen Top 100 cutoff. It does not establish an exact quarter-wide Reddit response count because the published Top 100 table does not expose below-cutoff rows.

For publishers, the responsible statement is therefore: Reddit was not detected at either matched endpoint and did not reach the published three-month Copilot Health Top 100 in this corpus. It should not be generalized into "Microsoft Copilot never cites Reddit."

For healthcare brands, providers, medical-device companies, senior-care businesses and CMOs, the practical implication is to prioritize the sources Copilot actually cites in the target health decision journey and validate Reddit against the brand's own prompt set rather than assuming Reddit importance transfers from ChatGPT, Gemini, Perplexity or Google's AI surfaces.

The surrounding Copilot Health source market is unusually broad and diffuse. The Top 10 account for only 18.5% of domain-response appearances, while the Top 100 account for 53.7%. Only 40 domains remained in the monthly Top 100 across July, August and September, and median monthly Top 100 Jaccard similarity was 38.9%.

Category specialization is substantial. Only 35 of Copilot's Health and Medical Top 100 domains also appear in Copilot's broader High-Stakes Consumer Decisions Top 100, a 21.2% Jaccard similarity. The final Health child-study Top 100 lists show Copilot sharing 41 domains with Google AI Overviews, 38 with Google AI Mode, 38 with Perplexity, 33 with Gemini and 32 with ChatGPT.

The broader Health and Medical Citation Authority Study reports 61.3% median monthly Top 100 persistence, 25.8% median cross-platform Top 100 portability, and an approximate 35.5 percentage-point Persistence-Portability Gap. The final six Health platform studies contain 290 distinct Top 100 domains in their union. Only 20 domains appear in all six platform Top 100s, while 161 appear in only one.

The Persistence-Portability Gap framework helps interpret Article 66 correctly. Health source authority is more persistent over time than universally portable across engines, while Copilot's own Health source market rotates more quickly. Article 66 should not create a Copilot-specific gap by subtracting 38.9% temporal persistence from one pairwise platform overlap because those comparison structures are different.

The parent Health and Medical Reddit decline study provides broader family context. Across the balanced all-platform Health family, Reddit citation-event share fell from 2.13% to 0.99%, down 53.5%, while response citation coverage fell from about 6.91% to 3.63%, down about 47.5%. Thirteen health verticals had both endpoint datasets, ten had measurable July Reddit event share, and all 10 of those 10 declined. Those are family-level results, not Copilot-specific balanced endpoint metrics.

Copilot also requires the most aggressive infrastructure cleanup in this Health platform family. The audited source study excludes 1,300 technical or navigational entries from the public publisher ranking: 1,105 bing.com, 181 bing.net, 12 bingapis.com and 2 openstreetmap.org entries. Microsoft's documentation confirms that Copilot can generate web-search queries and send them to the Bing search service to ground responses in web data, which helps explain why raw captures can contain search and navigation infrastructure that should not be interpreted as editorial publisher authority.

Citation visibility should remain separate from brand mentions, recommendation rate, rank, sentiment, citation-recommendation coupling, clinical quality, treatment safety and downstream business outcomes. A zero visible Reddit endpoint rate does not prove zero Reddit influence in training, latent model knowledge, retrieval or recommendation formation.

Commercial Action Matrix: What Publishers and CMOs Can Do With the Findings

Need company- or vertical-specific tracking? Publishers and companies can contact LLM Authority Index for individual vertical research, recurring AI citation tracking and company-level reporting. The research service does not sell rankings, inclusion or recommendation placement.

Where Article 66 Fits in the High-Stakes Consumer Decisions Corpus

Article 66 is a child analysis of two parent studies:

• the Health and Medical Reddit decline study, which provides the balanced family context, platform-specific matched comparison and broader replacement analysis; and
• the Microsoft Copilot Health and Medical source study, which provides the surrounding three-month source market, including the 53.7% Top 100 concentration, 40 domains present in all three monthly Top 100s and 38.9% median monthly Top 100 persistence.

The platform-level context comes from the overall Microsoft Copilot Top 100 study. The broader interpretation comes from the 2026 AI Citation Authority Study, the overall Reddit decline study, the cross-platform citation-overlap study, the citation-drift study, and the Persistence-Portability Gap framework. Those studies answer different questions and should not be collapsed into one visibility score.

The Core Matched Finding: Reddit Was Zero at Both Endpoints

Questions This Section Answers

• What happened when the exact prompt and Copilot platform were held constant?
• Were there any Reddit gains or losses?
• Can a percentage decline be calculated from zero to zero?

The strict matched analysis requires the same normalized prompt on the same Microsoft Copilot platform family to have one eligible analytical observation in July and one in September.

135 scenarios met that contract.

Matched Reddit response coverage is 0.00% in July and 0.00% in September.

There is no mathematically meaningful percentage decline from zero to zero.

Calling the result a 100% decline would be incorrect because there was no measured July Reddit baseline.

There are also no discordant pairs.

The correct matched statistical treatment is:

• losses: 0
• gains: 0
• loss-to-gain ratio: N/A
• exact McNemar p-value: N/A

The result is descriptive:

No Reddit citation transition in either direction was observed in the 135 matched Copilot health scenarios.

Why This Article Does Not Publish a Separate Copilot Aggregate Endpoint Percentage

Questions This Section Answers

• Why is there no Copilot-specific balanced July-to-September event-share table here?
• Is the metric unavailable or intentionally omitted?
• What evidence is used instead?

The parent Health and Medical Reddit study publishes:

• the balanced all-platform family endpoint;
• platform-specific matched counts and matched coverage;
• the all-platform replacement analysis; and
• the cross-platform matched comparison.

It does not publish a separate Microsoft Copilot aggregate July event share, September event share, July response coverage and September response coverage.

The supporting Copilot health source study publishes:

• three-month response coverage by domain;
• three-month citation events;
• source-market totals;
• monthly rank;
• monthly Top 100 persistence;
• category lift; and
• cross-platform Top 100 overlap.

It does not publish month-specific Reddit response counts because Reddit is not present in the public Top 100 table.

This article therefore does not infer or invent a platform-specific aggregate endpoint percentage.

The longitudinal claim is based on the verified 135-scenario matched panel.

The quarter-wide source-market claim is based on the verified 1,511-response Copilot health source study.

Copilot Still Produced the Largest Health Source Universe of the Six Platform Cuts

Questions This Section Answers

• Could the Reddit zero simply reflect a source-poor Copilot sample?
• How large was the underlying Copilot health citation market?
• Was Copilot actively citing external sources?

The Reddit non-detection did not occur in a sparse source environment.

The broader Copilot health source study contains:

A source market with 1,335 cited domains is not citation-poor.

Copilot was actively surfacing a broad mix of health publishers, consumer information sites, retail domains, senior-care resources, medical information sites and provider-related sources.

The Reddit zero is therefore a source-selection result inside an active market, not a consequence of little or no web citation activity.

Reddit Did Not Reach the Published Copilot Health Top 100

Questions This Section Answers

• Did Reddit appear as a meaningful three-month Copilot health source?
• What was the Top 100 cutoff?
• Can an exact quarter-wide Reddit count be inferred?

Reddit does not appear in the published Microsoft Copilot health Top 100.

The #100 domain, Planned Parenthood, appeared in 9 responses, equal to 0.60% response citation coverage.

That establishes that Reddit did not rank among the 100 most frequently cited registrable domains under the study's response-coverage ranking contract.

It does not establish an exact three-month Reddit count.

The frozen public source table does not include a below-cutoff Reddit row.

This article therefore does not infer one.

The supported statement is:

Reddit did not reach the published Copilot health Top 100.

Copilot's Leading Health Sources Were Strong and Persistent

Questions This Section Answers

• Which sources dominated Microsoft Copilot health answers?
• Did the leading source group remain visible month to month?
• How did their coverage compare with Reddit's non-detection?

The leading Copilot health sources were:

Forbes appeared in 156 responses.

Healthline appeared in 133.

NCOA.org appeared in 114.

Reddit did not reach the public Top 100 cutoff of nine responses.

That source hierarchy is materially different from ChatGPT, where Reddit was among the leading health sources in the pooled three-month market.

Copilot's Health Source Market Changed Month to Month

Questions This Section Answers

• Was the leading Copilot health source stable?
• How much did the monthly Top 100 change?
• Why should health brands track source drift?

The Copilot health source market changed materially across July, August and September.

Only 40 domains remained in the health Top 100 in all three months.

The leading source also changed.

• Forbes ranked #1 in July.
• Forbes ranked #1 in August.
• Google.com moved to #1 in September.
• Healthline ranked #2, #3 and #4.
• NCOA.org ranked #5, #2 and #3.

That movement shows that even a source market without measurable Reddit can still undergo significant citation drift.

Copilot's Health Source Market Was Highly Category-Specific

Questions This Section Answers

• How much did the health Top 100 overlap with Copilot overall?
• Would a broad Copilot source leaderboard capture the right healthcare publishers?
• Why does category-specific source mapping matter?

Only 35 of the health and medical Top 100 domains also appeared in Microsoft Copilot's broader High-Stakes Consumer Decisions Top 100.

That produces a Jaccard similarity of 21.2%.

The category effect is substantial.

Health-specific sources such as Healthline, NCOA.org, GoodRx, HelpGuide.org, HearingTracker and Audiologists.org have substantially higher measured coverage inside the health category than across Copilot's broader high-stakes corpus.

A broad platform authority list would therefore miss many health-specific citation opportunities.

Copilot's Health Top 100 Was Highly Distinct From Other AI Platforms

Questions This Section Answers

• How portable was health source authority between Copilot and other AI platforms?
• Which platform had the least overlap with Copilot?
• What does low overlap mean operationally?

The supporting source study compares the Microsoft Copilot health Top 100 with the other platform-specific health source maps.

Even the most similar platform shares only 41 Top 100 domains with Copilot.

ChatGPT shares only 32.

That fragmentation means a health publisher strategy optimized for ChatGPT is not automatically optimized for Microsoft Copilot.

It also helps explain why Reddit can be prominent in one health source market and absent in another.

Copilot Required the Largest Infrastructure Cleanup of the Health Platform Cuts

Questions This Section Answers

• How much technical citation infrastructure was removed?
• Which hosts accounted for the exclusions?
• Could infrastructure filtering explain the Reddit zero?

The deduplicated Copilot health slice contained 7,414 captured citation entries before public infrastructure filtering.

The public source ranking excludes:

After filtering, 6,114 substantive public-facing citation events remain.

The excluded infrastructure layer represents approximately 17.5% of captured citation entries before filtering.

That is a substantial cleanup requirement.

It does not create the Reddit non-detection.

After removing technical sources, Copilot still cited 1,335 registrable domains and produced 6,114 substantive citation events.

The source market remains broad enough that Reddit's absence is meaningful within the measured corpus.

Why Copilot Infrastructure Filtering Matters

Microsoft Copilot can expose Bing search, thumbnail, image, favicon, map and API-related source surfaces alongside substantive public publisher links.

Those technical surfaces should not be treated as evidence that Bing itself is an editorial authority on a health question.

The Copilot health source article explicitly audits and removes those entries before ranking public domains.

The audited public ranking therefore differs from an older parent category summary that displayed Bing among Copilot's leading domains.

For this Article 66, the audited child source study is the preferred publisher-market source because it applies the platform-specific cleanup required by the research plan.

Copilot's Reddit Pattern Was Completely Different From the Other Health Platforms

Questions This Section Answers

• Which health platforms had measurable Reddit baselines?
• Which platforms showed the strongest matched Reddit losses?
• Why is one blended Reddit KPI misleading?

The parent Health and Medical study reports:

Copilot is the only measured health platform with no matched Reddit baseline at either endpoint.

ChatGPT started from a very high matched Reddit baseline and nearly lost it.

Perplexity reached zero matched September coverage from a small baseline.

Gemini declined modestly from a low baseline.

Google's AI surfaces retained more Reddit continuity.

Copilot contributed no Reddit-positive matched cases in either month.

This is why a platform-neutral "Reddit visibility in AI" score can conceal more than it reveals.

The Parent Health Family Still Shows a Broad Reddit Decline

Questions This Section Answers

• Was the overall health family declining even though Copilot had no Reddit baseline?
• How large was the family-wide decline?
• How broad was the decline by vertical?

Across the balanced all-platform Health and Medical family, Reddit citation-event share fell from 2.13% to 0.99%, a 53.5% relative decline.

Response citation coverage fell from approximately 6.91% to 3.63%, down about 47.5%.

Thirteen health and medical verticals had both July and September datasets.

Ten had measurable Reddit citation-event share in July.

All 10 declined by September.

The median decline across those ten measurable verticals was 44.5%.

Those are all-platform family results.

They do not describe Microsoft Copilot's platform-specific endpoint because Copilot had no matched Reddit baseline in the first place.

No Single Publisher Replaced Reddit Across the Parent Health Study

Questions This Section Answers

• Did one source consistently replace Reddit?
• Which domains most often appeared after Reddit losses?
• Can those replacement results be attributed specifically to Copilot?

The parent health study examined 85 matched Reddit-loss scenarios across all tracked platforms.

The most common newly appearing domains were:

These are all-platform results.

They do not apply to Copilot's matched subset because Copilot contributed zero matched Reddit-loss scenarios.

There was no Reddit-positive Copilot matched case to replace.

Which Health and Medical Verticals Are Represented?

The full Microsoft Copilot health source study contains 14 source labels:

1. Addiction Treatment Centers
2. Assisted Living Facilities
3. Dental Implants
4. Fertility Clinics
5. Hearing Aids
6. Home Health Care
7. IVF Clinics
8. Medical Alert Systems
9. Mental Health Treatment Centers
10. Online Doctors
11. Online Pharmacies
12. Online Therapy
13. STD Tests
14. Weight Loss and Metabolic Health

Medical Alert Systems has no July source file in the frozen archive.

The parent balanced July-to-September health-family endpoint therefore uses 13 comparable verticals.

The three-month Copilot source ranking includes all 14 source labels.

How This Study Relates to Prior Copilot and Health Citation Research

Questions This Section Answers

• Does broad Copilot research also show a source market where Reddit is relatively weak?
• Why does Bing-related infrastructure matter when measuring Copilot citations?
• What does broader Q3 research say about social citation behavior across AI platforms?

Ahrefs' September 2026 broad U.S. Copilot study ranks Amazon #1 at 16.8% mention share across more than 3 million U.S. queries spanning all topics. Reddit does not appear in Ahrefs' published Top 50. That broad result is directionally compatible with Article 66's health-specific non-detection, but the two studies still use different query populations, denominators and ranking metrics.

Ahrefs defines mention share as a domain's citations divided by the summed citations of the Top 50 sources in its all-topic leaderboard. Article 66 instead measures high-stakes Health and Medical prompts using response citation coverage, public citation events and strict same-prompt matched persistence. The percentages should therefore not be merged.

Microsoft's own documentation says Microsoft Copilot and Copilot Chat can generate web-search queries and send them to the Bing search service to ground responses in current web data. That supports Article 66's decision to treat Bing search, network, API and navigation surfaces as a technical layer requiring separate classification rather than automatically counting every raw host as editorial publisher authority.

Tinuiti's Q3 2026 AI Citation Trends Report says most tracked AI platforms were at or near Q3 highs in social citation share, with Perplexity as a notable exception. Tinuiti tracks a different category mix, including OTC health, and measures broader social-source behavior rather than Reddit-only high-stakes Health citations. Its findings are useful platform context, but they should not be converted into a Copilot Health Reddit benchmark.

Taken together, the outside research reinforces a narrow conclusion: Copilot source behavior is highly dependent on query population, source-classification rules and the distinction between raw grounding infrastructure and public-facing publisher citations.

How This Study Relates to the Parent Health Reddit Study

The parent Health and Medical study found that Reddit's balanced all-platform citation-event share fell from 2.13% to 0.99%, a 53.5% relative decline.

Balanced response citation coverage fell from approximately 6.91% to 3.63%, down about 47.5%.

Across the all-platform strict matched panel, Reddit losses outnumbered gains 85 to 32.

Microsoft Copilot contributed:

• 0 losses
• 0 gains
• 0 persistent citations
• 135 neither-month scenarios

That produces matched coverage of 0.00% at both endpoints.

This child analysis therefore shows that Copilot did not drive the parent family's Reddit decline.

Instead, it represented a separate source environment where Reddit had no measurable matched baseline in either month.

How This Study Is Different

This article narrows the broader health Reddit research to one platform, one high-stakes family and one three-month research period.

It combines:

1. a 135-scenario strict matched prompt-plus-Copilot panel;
2. a 1,511-response three-month Microsoft Copilot Health and Medical source slice;
3. verified non-detection at both matched endpoints;
4. a source market containing 1,335 registrable cited domains;
5. explicit treatment of 1,300 Bing/OpenStreetMap technical and navigational entries;
6. category-overlap analysis showing only 35 shared domains with Copilot's broader Top 100;
7. cross-platform health Top 100 overlap analysis;
8. comparison with broad Copilot research from Ahrefs;
9. comparison with Tinuiti's Q3 platform findings; and
10. explicit disclosure that the parent source does not publish a separate Copilot balanced aggregate endpoint share.

The narrow research question is:

Was Reddit a stable, directly visible citation source in Microsoft Copilot for consequential health and medical consumer decisions from July through September 2026?

In the strict matched endpoint panel, Reddit was not measurable in either month.

Why AI Citation Studies Can Disagree

Questions This Section Answers

• Why can one Copilot study show no Reddit while another product surface may eventually surface it?
• Why can a three-month Top 100 differ from an endpoint matched panel?
• What should healthcare marketers compare before using an external benchmark?

Query population

High-stakes health prompts are not representative of all Microsoft Copilot questions.

Product surface

Different Copilot products can expose citations differently.

Web grounding

Retrieval behavior can vary by Copilot configuration.

Denominator

Matched response coverage, three-month source rank, citation-event share and external mention-share metrics answer different questions.

Source ranking cutoff

Reddit is outside the public Top 100, but that does not establish an exact three-month zero.

Technical-source cleanup

The public publisher ranking removes 1,300 Bing/OpenStreetMap technical and navigational entries.

Missing July data

Medical Alert Systems does not have a July source dataset and is excluded from the balanced parent family endpoint.

Prompt matching

The strict paired analysis requires the same normalized prompt and Microsoft Copilot platform family at both endpoints.

Prompt weighting

The panel is not weighted by patient volume, healthcare spend, search volume, CPC, revenue or conversion probability.

The correct conclusion is therefore conditional:

Reddit was not detected in this measured Microsoft Copilot health matched endpoint panel.

That is a strong empirical statement about the corpus.

It is not a universal product claim.

Methodology

Source archive

This study uses the frozen July-September 2026 LLM Authority Index High-Stakes Consumer Decisions corpus underlying the Health and Medical source studies and the parent health Reddit analysis.

Platform filter

Only observations assigned to the Microsoft Copilot platform family are used for the child platform analysis.

Category filter

Observations are included when their source membership belongs to the Health and Medical family.

Three-month Copilot health source sample

The supporting source study reports:

• 1,614 raw July-September Copilot health observations
• 0 explicit extraction failures
• 1,511 eligible deduplicated responses
• 7,414 captured citation entries before public infrastructure filtering
• 1,300 technical or navigational exclusions
• 6,114 substantive public-facing citation events
• 1,335 registrable cited domains
• 4,851 domain-response appearances

Exact analytical repeat handling

Exact analytical repeats are controlled using the project's documented repeat rules so duplicate observations do not inflate source coverage.

Prompt normalization

Matched prompt text is normalized using Unicode NFKC normalization, case folding, whitespace collapse and trimming.

Domain normalization

Citation URLs are parsed to hostname, lowercased, stripped of leading www where applicable and consolidated to registrable domain using Public Suffix List logic.

Reddit identification

Reddit is identified at the registrable-domain level as reddit.com.

Public technical exclusions

The Copilot health public ranking excludes:

• 1,105 bing.com entries
• 181 bing.net entries
• 12 bingapis.com entries
• 2 openstreetmap.org entries

Total excluded: 1,300.

Matched prompt-plus-platform test

The strict matched Copilot panel contains 135 scenarios.

The contingency table is:

• both July and September cite Reddit: 0
• July cites Reddit, September does not: 0
• July does not cite Reddit, September cites Reddit: 0
• neither month cites Reddit: 135

Matched response coverage is 0.00% in July and 0.00% in September.

Because there are no discordant pairs, a McNemar loss-versus-gain p-value is not applicable.

Three-month source-market context

The published Microsoft Copilot health Top 100 does not include Reddit.

The #100 domain appears in 9 responses, equal to 0.60% response citation coverage.

This article does not infer an exact below-cutoff Reddit three-month count that is not published in the source table.

Aggregate endpoint availability

The frozen parent study does not publish separate Microsoft Copilot balanced aggregate July and September citation-event share or response-coverage values.

Those values are therefore left unpublished rather than estimated.

Limitations

1. The strict matched Copilot panel contains no Reddit-positive cases at either endpoint.
2. A zero captured citation rate can reflect platform behavior, product-surface behavior, grounding configuration or collection mechanics.
3. The parent source does not publish a separate Copilot aggregate balanced endpoint share.
4. Reddit's exact three-month below-cutoff response count is not published and is not inferred here.
5. The three-month source ranking pools July, August and September.
6. Visible citation does not prove recommendation causality, hidden retrieval influence or training-data use.
7. Medical Alert Systems does not have a July source file and is excluded from the balanced parent endpoint.
8. Domain-level aggregation hides page-level source differences.
9. Technical-source cleanup is especially important for Copilot because 1,300 infrastructure/navigation entries were excluded.
10. Microsoft Copilot behavior can vary by product surface, geography, account state, model version and retrieval configuration.
11. The all-platform replacement table should not be interpreted as a Copilot-only replacement analysis.
12. The study does not evaluate the medical quality or clinical reliability of Reddit content.

Commercial Disclosure

LLM Authority Index is affiliated with CiteWorks Studio and related AI-search research and services. This research documents observed AI citation behavior.

Commercial relationships do not alter the frozen source corpus, platform filter, category filter, matching contract or published denominators.

No company can purchase a ranking, recommendation, score or position in this study. Citation visibility should not be interpreted as an endorsement by LLM Authority Index or Microsoft.

References

1. LLM Authority Index: The 2026 AI Citation Authority Study
2. LLM Authority Index: The Most-Cited Websites in AI for High-Stakes Health and Medical Consumer Decisions
3. LLM Authority Index: Reddit's Decline in AI Citations for High-Stakes Health and Medical Consumer Decisions
4. LLM Authority Index: The 100 Most-Cited Websites in Microsoft Copilot for High-Stakes Health and Medical Consumer Decisions
5. LLM Authority Index: The Persistence-Portability Gap
6. LLM Authority Index: The 100 Most-Cited Websites in Microsoft Copilot for High-Stakes Consumer Decisions
7. Ahrefs: The 50 Most-Cited Websites in Copilot, September 2026
8. Tinuiti: Q3 2026 AI Citation Trends Report
9. Microsoft Learn: Data, privacy, and security for web search in Microsoft Copilot and Microsoft Copilot Chat

Related LLM Authority Index Research

Corpus foundation and measurement framework

• 2026 AI Citation Authority Study
• Overall Reddit Citation Decline Study
• Cross-Platform Citation Overlap Study
• AI Citation Drift Study
• Overall Microsoft Copilot Top 100 Study
• Persistence-Portability Gap Framework

Health and Medical source-market branch

• All-Platform Health and Medical Citation Authority Study
• Google AI Overviews Health and Medical Citation Sources
• Google AI Mode Health and Medical Citation Sources
• ChatGPT Health and Medical Citation Sources
• Perplexity Health and Medical Citation Sources
• Gemini Health and Medical Citation Sources
• Microsoft Copilot Health and Medical Citation Sources

Health and Medical Reddit-trend branch

• Health and Medical Reddit Decline Parent Study
• Google AI Overviews Reddit Trend
• Google AI Mode Reddit Trend
• ChatGPT Reddit Trend
• Perplexity Reddit Trend
• Gemini Reddit Trend
• Microsoft Copilot Reddit Trend