Statutory changes to Mental Health Diversion in California have introduced an important shift: nexus between mental illness and the charged offense is presumed unless there is clear and convincing evidence that mental health did not play a role.
This change has understandably generated confusion, particularly regarding the role of the forensic psychologist. Some assume that a legal presumption of nexus relieves evaluators of the need to independently analyze whether mental health symptoms actually contributed to the alleged behavior.
It does not.
Legal Presumptions Do Not Eliminate Forensic Analysis
A legal presumption serves a procedural purpose. It does not replace the ethical and professional obligations of a forensic evaluator.
Even where the law presumes mental illness was a contributing factor, a psychologist still has a duty to:
conduct an independent evaluation,
analyze the available evidence,
and articulate whether a logical, evidence-based connection exists between symptoms and behavior.
Forensic opinions cannot rest solely on statutory language. They must be grounded in data.
The Ethical Obligation to Analyze Nexus
As forensic psychologists, we are not permitted to assume nexus simply because a diagnosis or mental health history exists. Our ethical obligations require us to evaluate whether there is actual evidence that symptoms meaningfully contributed to the behavior at issue.
That analysis includes examining:
the timing and severity of symptoms,
functional impairment at the relevant time,
consistency across records and collateral sources,
and alternative, non-psychiatric explanations for behavior.
Where the evidence does not support a clear, functional connection, an evaluator cannot responsibly endorse a nexus opinion solely on the basis of statutory presumption.
Why This Matters in Reports and Testimony
Forensic opinions do not exist only on paper. They must be defensible under oath.
If called to testify, an evaluator must be able to explain:
how the opinion was reached,
what evidence supports it,
and why alternative explanations were accepted or rejected.
Testimony cannot rest on a presumption alone. A psychologist must be able to identify the evidence supporting the conclusion that mental illness meaningfully contributed to the behavior. When such evidence is absent, the ethical course is to say so.
Presumption Does Not Mean Automatic Causation
This is where frustration often arises.
Even when an individual has a documented history of mental health issues, those issues are not always contributing factors to every instance of alleged criminal behavior. Some conduct is better explained by situational stressors, interpersonal conflict, or goal-directed decision-making.
Recognizing that distinction is not dismissive of mental illness. It is central to responsible forensic practice.
The Practical Reality Since the Code Change
Since the statutory change, evaluators and attorneys alike have been navigating this tension between legal presumption and forensic analysis.
From the evaluator’s perspective, the obligation remains the same: to “flesh everything out,” examine the available information, and provide an opinion that can withstand scrutiny in court.
Where the evidence supports nexus, it should be clearly articulated. Where it does not, that absence must also be clearly explained.
A Final Clarification
A conclusion that nexus is not supported by the available evidence is not a rejection of the law, nor is it an adversarial stance. It reflects the limits of what a forensic psychologist can responsibly say based on the information available at the time of the evaluation.
Legal presumptions guide procedure. Ethical obligations govern professional opinion.
Understanding the distinction between the two is essential to the effective use of forensic psychological evaluations in Mental Health Diversion matters.
