What Does "At Least as Likely as Not" Mean in a VA Medical Nexus Opinion?

Quick Answer

"At least as likely as not" is terminology commonly used in VA medical-opinion practice. A clinician uses it to express a supportive medical probability conclusion: that, in the clinician's professional judgment, the claimed relationship between the condition and service (or a service-connected disability) is at least as probable as not.

That terminology describes the clinician's medical conclusion. It is separate from the adjudicative standard VA applies to the record as a whole. Under 38 U.S.C. § 5107(b) and 38 CFR § 3.102, when the positive and negative evidence regarding a material issue are in approximate balance, the benefit of the doubt is given to the claimant. The Federal Circuit in Lynch v. McDonough described approximate balance as evidence that is nearly equal.

Speculative or equivocal wording may reduce the usefulness or probative value of a medical opinion, particularly when the clinician does not express a sufficiently definite medical conclusion or provide reasoning explaining the relationship being evaluated. Medical certainty, however, is not required.

You May Have Seen Language Like This

What Does This Mean?

It helps to separate two different things: the terminology a clinician uses to express a medical conclusion, and the way VA adjudicators then evaluate the complete evidentiary record.

1. Supportive medical conclusions: A clinician who concludes that the claimed relationship is at least as likely as not - or more likely than not - is expressing a conclusion that supports the claimed relationship.
2. Unfavorable medical conclusions: A clinician who concludes that the claimed relationship is less likely than not is expressing a conclusion that does not support the claimed relationship.
3. Speculative or equivocal conclusions: Wording such as "is possible," "may be," "cannot rule out," or "could potentially be" may reduce the usefulness or probative value of an opinion, particularly when the clinician does not express a sufficiently definite medical conclusion or provide reasoning explaining the relationship being evaluated.
4. Medical Certainty Not Required: Medical certainty is not required for a medical opinion to be considered. Clinicians provide medical conclusions based on their professional judgment, the veteran's relevant history, clinical findings, and applicable medical principles. VA adjudicators then evaluate those opinions in the context of the complete evidentiary record.
5. The adjudicative question is different: Adjudicators do not perform a numerical calculation. They weigh the evidence as a whole, and the benefit-of-the-doubt rule applies when the positive and negative evidence regarding a material issue are in approximate balance.

Open Your VA Decision and Check These Things

• The Exact Phrasing Used by the Examiner: Does the decision quote the specific probability language used in the C&P exam report?
• The Phrasing in Your Private Medical Opinion: Did your private medical nexus letter express a definite medical conclusion, or did it use uncertain wording such as "could" or "might"?
• The Underlying Medical Rationale: Even if a clear conclusion was stated, did VA find the supporting explanation (the "rationale") inadequate?
• Factual Foundation: Did the clinician state the conclusion based on a complete and accurate review of your medical and service history?
• Conflicting Conclusions: Did the C&P examiner conclude "less likely than not" while your private doctor concluded "at least as likely as not"?

Questions to Consider

• Did your private medical opinion express a definite medical conclusion, or did it describe the relationship as a possibility?
• If the private clinician used the phrase "at least as likely as not," did the decision explain why that opinion was not found persuasive?
• Did the C&P examiner explain why they concluded the condition was "less likely than not" related to service?
• Was the denial based on the terminology itself, or on the adequacy of the clinical reasoning supporting the conclusion?

What Authoritative Sources Say

• 38 U.S.C. § 5107(b): The statutory benefit-of-the-doubt rule, establishing that when there is an approximate balance of positive and negative evidence regarding any issue material to the determination, the Secretary shall give the benefit of the doubt to the claimant.
• 38 CFR § 3.102: The reasonable doubt doctrine, clarifying that when reasonable doubt arises regarding the degree of disability, service connection, or any other point, that doubt will be resolved in favor of the claimant.
• 38 CFR § 4.3: Confirms that in rating evaluations, where reasonable doubt arises, that doubt is to be resolved in favor of the claimant.
• Gilbert v. Derwinski, 1 Vet. App. 49 (1990): Foundational CAVC decision explaining the unique standard of proof in veterans law and the operation of reasonable doubt.
• Lynch v. McDonough, 21 F.4th 776 (Fed. Cir. 2021) (en banc): Confirmed that under 38 U.S.C. § 5107(b), the benefit-of-the-doubt rule operates where the positive and negative evidence are in approximate balance, described as nearly equal.

What This Does Not Necessarily Mean

• It does not mean simply using particular words guarantees approval. Stating a conclusion without providing a supporting clinical explanation connecting the facts of the case to medical principles does not make an opinion probative.
• It does not mean medical certainty is required. A clinician is not expected to prove a causal link with absolute scientific certainty.
• It does not mean the evidence was in approximate balance if one opinion was found more probative. If an adjudicator determines that one opinion is supported by stronger clinical rationale and factual foundation, the adjudicator may conclude the evidence is not in approximate balance.

When This May Be a Medical Question

Whether a clinician can support a claimed relationship is a matter of clinical judgment:

• Assessing Plausibility vs. Probability: A clinician must distinguish between what is biologically possible in a general population and what is clinically probable in a specific veteran's case.
• Connecting Facts to Conclusions: The clinician must bridge the veteran's specific records and clinical findings with established medical literature or pathophysiology.
• Addressing Counter-Theories: A persuasive opinion often explains why alternative medical explanations or risk factors do not outweigh the relationship being evaluated.

Is More Medical Evidence Actually Needed?

More medical evidence may be helpful if:

• A previous nexus letter was discounted specifically because it used uncertain wording such as "could be" or "might be" rather than a definite medical conclusion.
• The previous opinion stated a clear conclusion but did not provide the detailed medical reasoning explaining why.
• The C&P examiner concluded "less likely than not" based on an incomplete medical history that a new clinical evaluation could address.

More medical evidence may not be needed if:

• The private opinion already contained a clear conclusion with thorough rationale, but the adjudicator did not address it in the decision narrative.
• The denial was based on a non-medical requirement, such as lack of qualifying military service.

Questions to Ask Your VA-Accredited Representative

• "Did VA discount my private medical opinion because of the terminology used, or because of the supporting rationale?"
• "Did the C&P examiner state that my condition was 'less likely than not' related to service, and what reasons did the examiner give?"
• "If my private doctor used uncertain or speculative language, would additional medical clarification be useful, or is the primary issue how VA evaluated the existing opinion?"
• "Does the record present an approximate balance of positive and negative evidence on a material issue?"