The “At Least As Likely As Not” Standard Explained

The 50% Threshold That Determines Your VA Claim

You’ve gathered your medical records, submitted your claim, and waited months for a decision. Then you read the VA’s denial letter: “It is less likely than not that your condition is related to service.” What does that even mean? How did the VA measure “likely” versus “less likely,” and why does this phrase appear in nearly every service connection decision?

The answer lies in understanding the VA’s burden of proof standard: “at least as likely as not.” This legal threshold determines whether your claim succeeds or fails, and knowing how it works—and how medical evidence must address it—can be the difference between approval and denial.

What Does “At Least As Likely As Not” Mean?

The phrase “at least as likely as not” is the VA’s way of expressing a probability threshold of 50% or greater.

In legal terms, this is called the “burden of proof”—the level of certainty required to prove your claim. Different types of legal claims use different standards:

• Criminal cases: “Beyond a reasonable doubt” (approximately 95-99% certainty)
• Most civil cases: “Preponderance of the evidence” (more than 50%)
• VA disability claims: “At least as likely as not” (50% or greater)

The VA standard is veteran-friendly. You don’t have to prove your claim beyond a reasonable doubt or even with overwhelming certainty. You just need to show that it’s at least as probable as not that your condition is related to military service.

In practical terms:

• If there’s a 51% chance your PTSD is caused by service and 49% chance it’s not, you meet the standard. ✅
• If there’s a 50-50 chance (equal probability), you meet the standard. ✅
• If there’s a 49% chance it’s service-related and 51% chance it’s not, you don’t meet the standard. ❌

This is why the exact language used in psychiatric medical opinions is critical. Phrases like “possibly,” “could be,” or “maybe” don’t establish a 50% threshold. The psychiatric medical opinion must affirmatively state that it is “at least as likely as not” that your condition is service-related.

History and Origin of the “At Least As Likely As Not” Standard

The “at least as likely as not” standard did not appear overnight. It grew out of decades of federal policy designed to honor the unique obligation the United States owes to those who served in uniform.

The legal foundation sits in 38 C.F.R. § 3.102, the regulation that codifies the “benefit of the doubt” doctrine for VA claims. This regulation states that when the evidence for and against a claim is in approximate balance, reasonable doubt is resolved in the veteran’s favor. Congress reinforced this principle in 38 U.S.C. § 5107(b), making it statutory law — not merely an agency guideline that the VA could revoke on its own.

The doctrine reflects what legal scholars call equipoise — the point where the scales of evidence are evenly balanced. What makes the VA standard uniquely veteran-favorable is this: in a civil lawsuit, a perfect 50/50 split means the plaintiff loses because they have not tipped the scales past the midpoint. In a VA claim, that same 50/50 split means the veteran wins. Congress designed it this way deliberately, recognizing that military service creates hazards and hardships that civilian life does not, and that service records are often incomplete through no fault of the veteran.

Understanding this history matters because it reveals the intent behind the language. The phrase “at least as likely as not” is not clinical jargon — it is a precise legal term mapped to a specific probability, and every word carries weight in the adjudication process.

The 50% Threshold in VA Claims

The “at least as likely as not” standard comes from the law governing VA claims. It reflects the VA’s mission to give veterans the benefit of the doubt when evidence is evenly balanced.

Key Principle: Benefit of the Doubt

Under 38 U.S.C. § 5107(b), when evidence is in “approximate balance,” the VA must resolve reasonable doubt in favor of the veteran. This means if the evidence is roughly 50-50, the claim should be granted.

In practice, this principle means:

• You don’t need overwhelming proof
• Gaps in service medical records shouldn’t automatically lead to denial
• When psychiatric medical opinions conflict, the VA should weigh them fairly and resolve doubt in your favor

However, there’s a catch:

The benefit of the doubt only applies when evidence is approximately equal on both sides. If the VA examiner says your condition is “less likely than not” service-related, and you have no contradicting medical evidence, there’s no approximate balance—there’s just a negative opinion.

This is why veterans need strong psychiatric medical opinions that affirmatively meet the “at least as likely as not” standard. You can’t rely on benefit of the doubt if the evidence is one-sided against you.

How VA Raters Interpret the Phrase in Practice

Understanding the standard on paper is one thing. Understanding how VA Rating Veterans Service Representatives (RVSRs) and Board of Veterans’ Appeals (BVA) judges actually apply it is another.

Raters look for explicit language first. When a rater opens a medical opinion, the first thing they scan for is whether the physician used the “at least as likely as not” phrase — or an equivalent like “more likely than not” or “to a reasonable degree of medical probability.” If that phrase is absent, the opinion may be set aside before the rationale is even read. This is not because raters are rigid — it is because they must document that the evidentiary standard was met, and ambiguous language creates audit risk.

Rationale quality determines probative weight. Even when the correct language is present, raters weigh the quality of the reasoning behind it. A one-sentence conclusion without supporting analysis carries far less weight than an opinion that walks through the veteran’s service records, identifies specific in-service stressors or injuries, connects those events to current symptoms using medical literature, and addresses any evidence that cuts against the conclusion. BVA decisions routinely describe why one opinion was given “greater probative weight” over another, and the distinguishing factor is almost always the depth and specificity of the rationale.

Competing opinions force a weighing analysis. When a C&P examiner says “less likely than not” and a private IMO says “at least as likely as not,” the rater cannot simply pick one. Regulations require the rater to consider each physician’s qualifications, the thoroughness of the record review, the adequacy of the rationale, and whether each opinion addresses all relevant evidence. An IMO from an ABPN Board-Certified psychiatrist who reviewed the complete claims file and cited peer-reviewed literature will typically outweigh a brief C&P opinion based on a 30-minute interview and incomplete records.

Common examiner pitfalls that undercut claims. Raters frequently encounter opinions using phrases like “possibly related,” “could be connected,” or “cannot be ruled out.” These formulations suggest a probability below 50% and do not trigger the benefit-of-the-doubt doctrine. Veterans who receive opinions with this language should consider obtaining an Independent Medical Opinion that provides the definitive language the VA requires.

How Medical Opinions Establish This Standard

When you submit an Independent Medical Opinion (IMO) or undergo a VA compensation and pension (C&P) examination, the physician must address the nexus between your condition and military service. The language they use matters enormously.

Language That DOES Meet the Standard:

• “It is at least as likely as not that the veteran’s condition is related to service.”
• “To a reasonable degree of medical probability, this condition was caused by military service.”
• “It is more likely than not that this condition is service-connected.”
• “Based on my review of the evidence, I conclude with greater than 50% medical probability that this condition is related to service.”

Language That DOES NOT Meet the Standard:

• “The veteran’s condition could be related to service.” ❌
• “It is possible that service contributed to this condition.” ❌
• “This condition may have been caused by military service.” ❌
• “I cannot rule out a service connection.” ❌

The difference is probability. “Could be” and “possible” suggest something less than 50%. “At least as likely as not” clearly states a 50% or greater probability.

Example: A Weak Nexus Opinion

“The veteran reports developing depression after leaving the military. It is possible that his depression is related to his service experiences. However, depression can have many causes, and I cannot definitively determine the cause in this case.”

Why This Fails: The language “possible” and “cannot definitively determine” suggests the physician is uncertain and cannot commit to a 50% probability. The VA will interpret this as not meeting the standard.

Example: A Strong Nexus Opinion

“Based on my comprehensive review of the veteran’s service records, medical history, and clinical examination, it is my opinion to a reasonable degree of medical certainty (greater than 50% probability) that the veteran’s current major depressive disorder is at least as likely as not caused by his service-connected chronic pain condition. The medical literature clearly establishes chronic pain as a significant risk factor for depression. The temporal relationship between the veteran’s pain condition and the onset of depressive symptoms, combined with the well-documented pain-depression pathway, supports this conclusion.”

Why This Succeeds: The physician explicitly states a greater than 50% probability, uses the “at least as likely as not” language, and provides medical rationale supporting the conclusion.

“At Least As Likely As Not” vs. “More Likely Than Not” — A Critical Distinction

Veterans and even some medical professionals confuse these two phrases, assuming they are interchangeable. While both can support a successful claim, they represent different probability thresholds — and understanding the difference matters when reviewing your medical evidence.

	“At Least As Likely As Not”	“More Likely Than Not”
Probability threshold	50% or greater (includes exact 50/50)	Greater than 50% (excludes exact 50/50)
Legal meaning	The condition is equally or more probable than not to be service-connected	The condition is more probable than not to be service-connected
Who it favors	Maximum veteran benefit — wins at the tie	Also veteran-favorable, but sets a slightly higher bar
When used	Standard VA nexus language; the phrase VA raters look for most often	Acceptable alternative; commonly used in medical-legal opinions
Benefit-of-the-doubt impact	Explicitly captures the 50/50 equipoise scenario where the veteran prevails	Implicitly exceeds the equipoise threshold
Risk	None — this is the gold standard phrase	Minimal, but some raters may note it does not use the VA’s preferred phrasing

The practical takeaway: “At least as likely as not” is the preferred language because it maps precisely to the VA’s legal standard and explicitly covers the 50/50 equipoise scenario. “More likely than not” is also acceptable and meets the threshold, but “at least as likely as not” leaves zero room for misinterpretation. When Dr. Lee prepares an IMO through VetNexusMD, the opinion uses “at least as likely as not” as the primary standard because it is the exact language VA raters are trained to look for.

If you are reviewing a nexus letter for your Florida-based claim or any other state, confirm that the opinion uses one of these two formulations — never “possibly,” “could be,” or “may be.”

Common Pitfalls in Meeting This Standard

Many veterans submit medical evidence that seems supportive but doesn’t actually meet the legal threshold. Understanding these common mistakes can help you avoid them.

Pitfall #1: Treating Physician Letters That Are Too General

Your treating doctor writes: “In my opinion, this veteran’s PTSD is related to his military service.”

While this sounds positive, it doesn’t use the required “at least as likely as not” language. More importantly, if the doctor doesn’t explain why they reached this conclusion and doesn’t review service records, the VA may give the opinion little weight.

Solution: Request that psychiatric medical opinions specifically use the “at least as likely as not” language and include medical rationale with record citations.

Pitfall #2: Equivocal Statements

A C&P examiner writes: “The veteran’s PTSD could be related to his combat deployment, but it could also be due to pre-existing anxiety tendencies.”

This is an equivocal opinion—it doesn’t commit to a probability. The VA will interpret this as not meeting the 50% threshold.

Solution: Submit an Independent Medical Opinion that reviews the same evidence and provides a definitive opinion meeting the standard.

Pitfall #3: Negative VA Examinations Without Rebuttal

The VA examiner concludes: “It is less likely than not that the veteran’s depression is related to service.”

Many veterans accept this as final. It’s not. You can submit a contradicting psychiatric medical opinion from a private physician. If your IMO provides superior medical reasoning and more complete record review, the VA must weigh it against the examination.

Solution: Don’t give up after a negative C&P exam. Get a second opinion from a qualified specialist.

Pitfall #4: Lay Statements Without Medical Support

You write a statement: “I believe my anxiety disorder developed from the combat stress I experienced in Iraq.”

Lay evidence is valuable for describing symptoms and events, but veterans are not competent to provide medical nexus opinions. You can describe what happened and when symptoms began, but you need a medical professional to establish the medical connection.

Solution: Use lay statements to document facts (when symptoms started, what service events occurred), and obtain psychiatric medical opinions to establish the nexus.

Common Mistakes That Sink Nexus Letters

Beyond the pitfalls described above, there are structural errors that cause otherwise supportable claims to fail at the nexus-letter stage. If you are preparing to submit an IMO or working with a physician on one, watch for these issues.

Mistake #1: Vague or conclusory rationale. Stating “it is at least as likely as not that the veteran’s depression is related to service” without explaining why is insufficient. VA raters and BVA judges require a medical reasoning chain — what happened in service, how it connects to the current condition, and what medical principles or literature support that connection. A conclusion without a rationale is like a verdict without a trial. For a deeper look at the documentation process, see our guide to how the IMO process works.

Mistake #2: Ignoring negative evidence. Every claims file contains evidence that could cut both ways. A strong IMO acknowledges and addresses unfavorable facts — a gap in treatment, a pre-service history of symptoms, or an alternative cause raised by a C&P examiner. Ignoring these issues does not make them disappear; it signals to the rater that the physician either did not review the full record or chose to avoid inconvenient evidence. BVA decisions consistently give less weight to opinions that do not engage with negative evidence.

Mistake #3: Using equivocal language. Words like “might,” “could,” “possibly,” and “perhaps” are clinical hedges that feel natural in a treatment setting but are fatal in a legal opinion. Each of these terms implies a probability below 50%. Even “likely” standing alone can be ambiguous. The opinion must use “at least as likely as not,” “more likely than not,” or “to a reasonable degree of medical probability” — language that maps to the 50% threshold without ambiguity.

Mistake #4: Failing to cite medical literature. A nexus opinion grounded in peer-reviewed research is substantially more persuasive than one based solely on clinical experience. For example, a PTSD nexus letter that cites the established literature on combat-related trauma and delayed-onset PTSD provides the rater with an independent basis to credit the opinion. Medical literature citations transform an opinion from “this doctor thinks so” into “the medical community recognizes this connection.”

Mistake #5: Not reviewing the complete service record and claims file. An IMO based on a veteran’s self-reported history alone — without review of service treatment records, personnel records, VA examination reports, and prior rating decisions — is vulnerable to challenge. At VetNexusMD, Dr. Lee — a Harvard-trained, ABPN Board-Certified psychiatrist — conducts a comprehensive review of every document in the claims file before forming an opinion. Records are submitted through our secure CharmHealth portal, ensuring a complete and organized review.

Key Takeaways

• “At least as likely as not” means 50% probability or greater. This is the VA’s burden of proof for service connection claims.
• Exact language matters. Psychiatric medical opinions must use phrases like “at least as likely as not” or “more likely than not,” not “possible” or “could be.”
• Medical rationale is required. It’s not enough to state a conclusion—the physician must explain the medical reasoning supporting the 50% probability.
• The benefit of the doubt applies when evidence is balanced. If you have no positive medical evidence, you can’t rely on benefit of the doubt.
• Negative VA examinations can be countered. Submit Independent Medical Opinions that meet the standard and provide superior analysis.

How VetNexusMD Can Help

At VetNexusMD, Dr. Ronald Lee understands exactly how to craft psychiatric medical opinions that meet the VA’s “at least as likely as not” standard. Every Independent Medical Opinion Dr. Lee provides includes:

• Explicit use of VA-compliant language (“at least as likely as not,” “greater than 50% medical probability”)
• Detailed medical rationale explaining the clinical basis for the opinion
• Comprehensive review of service records, VA examinations, and treatment history
• Citations to medical literature where appropriate
• Board-certified expertise in psychiatry for mental health claims

Whether you’re filing an initial claim or appealing a denial based on a negative VA examination, Dr. Lee’s IMOs are designed to meet the legal and medical requirements the VA demands.

Learn more about our Independent Medical Opinion services or request a consultation today.

Frequently Asked Questions

What if my VA examiner used the phrase “less likely than not”?
This means the examiner concluded there is less than a 50% probability your condition is service-related. This does not automatically mean your claim is denied—you can submit contradicting medical evidence. An Independent Medical Opinion from a qualified specialist can provide a different conclusion based on more thorough record review or superior medical reasoning.

Can I use the phrase “more likely than not” instead of “at least as likely as not”?
Yes. “More likely than not” means greater than 50%, which meets the standard. Both phrases are acceptable. The key is clearly establishing a probability of 50% or higher.

Does my doctor need to use the exact phrase “at least as likely as not”?
While using the exact phrase is ideal, what matters is clearly expressing a probability of 50% or greater. Phrases like “to a reasonable degree of medical certainty,” “more likely than not,” or “with greater than 50% medical probability” can also meet the standard if properly explained.

What if two psychiatric medical opinions conflict—one says “at least as likely as not” and one says “less likely than not”?
The VA must weigh both opinions. They’ll consider the physicians’ qualifications, the thoroughness of record review, the quality of medical reasoning, and whether the opinions address all relevant evidence. A well-reasoned IMO from a board-certified specialist often carries more weight than a brief C&P examination.

Can I submit multiple psychiatric medical opinions supporting my claim?
Absolutely. If you have treating physician letters, specialist opinions, and an Independent Medical Opinion all supporting your claim, submit them all. More evidence is generally better, as long as it’s relevant and meets the “at least as likely as not” standard.

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VetNexusMD provides Independent Medical Opinions based on thorough medical record review. We do not establish doctor-patient treatment relationships or guarantee VA claim outcomes. Our service is to deliver expert psychiatric medical opinions that meet VA evidentiary standards.

Additional Frequently Asked Questions

What does “at least as likely as not” mean?
“At least as likely as not” means there is a 50% or greater probability that a veteran’s condition is related to military service. This is the VA’s standard of proof for establishing service connection, codified in 38 C.F.R. § 3.102. It reflects the benefit-of-the-doubt doctrine — when evidence is evenly balanced, the decision goes in the veteran’s favor. A physician must use this specific language (or an equivalent like “more likely than not”) in a nexus opinion to meet the VA’s requirements.

What is the “at least as likely as not” standard in VA claims?
It is the legal threshold that medical opinions must meet to establish a nexus — the connection between a current condition and military service. Unlike criminal cases (proof beyond a reasonable doubt) or civil lawsuits (preponderance tipping past 50%), the VA standard grants the veteran the benefit at the exact 50/50 point. For veterans pursuing mental health claims, this standard applies to every service-connection determination.

What is the equipoise doctrine in VA disability?
The equipoise doctrine (also called the “benefit of the doubt” rule) means that when evidence supporting a VA claim is in approximate balance with evidence against it, the doubt is resolved in the veteran’s favor. It is codified at 38 U.S.C. § 5107(b) and 38 C.F.R. § 3.102. A veteran does not need to prove their case by a majority of the evidence — reaching a roughly even split is sufficient. The equipoise doctrine is the legal foundation behind the “at least as likely as not” language in nexus opinions.

What standard of proof is needed for a nexus letter?
A nexus letter must establish that it is “at least as likely as not” (50% probability or greater) that the veteran’s condition is connected to military service. The physician must use this language or a clear equivalent, provide a detailed medical rationale, cite relevant service records and medical literature, and address evidence that weighs against the conclusion. Veterans pursuing claims involving military sexual trauma or other sensitive conditions should work with a specialist who understands both the medical and legal dimensions of this standard.

What is the 50/50 rule in VA claims?
The “50/50 rule” is an informal name for the benefit-of-the-doubt doctrine. When the evidence for and against service connection is evenly split — a true 50/50 — the veteran wins. This differs from most legal proceedings, where a 50/50 split means the party with the burden of proof loses. The phrase “at least as likely as not” includes “at least” precisely to capture both the equal-probability scenario and any probability above 50%. If you have questions about whether your evidence meets this standard, call VetNexusMD at (617) 506-3411.

Related Reading

Understanding the “at least as likely as not” standard is essential for building strong VA claims. Here are additional resources to help you navigate the process:

Nexus Letters & Medical Evidence

• What is a Nexus Letter? – Learn the fundamentals of nexus letters and why they’re critical for your claim
• Understanding Nexus Letters: Your Key to VA Claim Success – A comprehensive guide to obtaining effective medical evidence

Secondary Conditions & Rating Increases

• Secondary Conditions: Hidden Opportunities for Increased VA Ratings – Discover conditions that may qualify for additional compensation
• 2025 VA Rating Changes: Mental Health Updates You Need to Know – Stay current on the latest rating criteria

Condition-Specific Guides

• Anxiety VA Disability: Complete Rating Guide
• PTSD and VA Disability: Complete Guide
• VA Nexus Letter Guide: Everything Veterans Need to Know
• VA Mental Health Ratings Explained
• PTSD Complete Guide for Veterans

PTSD Claims Guide

For a detailed guide on obtaining nexus letters specifically for PTSD claims, see: PTSD Nexus Letters: The Complete Guide to Strengthening Your VA Disability Claim.