The key finding
A 2025 systematic review examining how different countries assess whether someone has the mental capacity to make a valid will found striking inconsistencies in both legal standards and medical evaluation methods. The analysis revealed that jurisdictions worldwide lack standardized approaches for determining testamentary capacity—the cognitive ability required to understand what you’re doing when creating or changing a will. This variability is particularly problematic for individuals with dementia or psychiatric conditions, where cognitive abilities may fluctuate. Some legal systems recognize “lucid intervals” during which a person with dementia might temporarily regain sufficient mental clarity to execute a will, while others apply more rigid standards.
What the study looked like
Researchers conducted a systematic review following PRISMA guidelines, searching three major databases (PubMed, Scopus, and Web of Science) plus grey literature from Google Scholar. They focused on studies addressing testamentary capacity assessments, cognitive evaluation methods, bioethical considerations, and legal frameworks across multiple countries. The search used Boolean keyword combinations relating to testamentary capacity, dementia, cognitive assessment, and bioethics. The review included studies that provided specific measures for evaluating testamentary capacity and discussed bioethical implications. Rather than collecting new patient data, this review synthesized existing research to map the landscape of how different jurisdictions approach this complex intersection of law, medicine, and ethics.
Why researchers think this happened
The researchers identified several factors contributing to international variability in testamentary capacity assessments. Historical legal precedents continue to shape modern practice—particularly the 1870 English case Banks v Goodfellow, which established criteria still referenced today in many jurisdictions. However, medical understanding of cognitive decline has evolved considerably since the 19th century. The concept of “lucid intervals” in dementia patients reflects growing recognition that cognitive abilities can fluctuate rather than declining uniformly. Deathbed wills present particular challenges because diminished cognitive functioning near life’s end complicates capacity evaluations. The emergence of neurolaw—applying neuroscience to legal questions—has provided new frameworks for understanding decision-making capacity. Recent developments in artificial intelligence offer potential assessment tools but also raise novel ethical questions about algorithmic decision-making in sensitive legal contexts.
How to read this carefully
This review highlights variability in assessment approaches rather than establishing which methods work best. The included studies likely vary in quality, sample sizes, and cultural contexts, making direct comparisons difficult. The legal standards discussed reflect specific jurisdictions and may not apply universally. “Lucid intervals” remain controversial—while some research suggests cognitive abilities can temporarily improve in dementia patients, determining when someone has sufficient capacity to make consequential legal decisions remains subjective. The review doesn’t provide outcome data showing which assessment methods best predict valid decision-making or prevent exploitation. The discussion of AI in capacity assessments is forward-looking; these technologies aren’t yet validated for this sensitive application. Readers should recognize that testamentary capacity assessment involves professional judgment combining legal, medical, and ethical considerations—not a simple checklist.
What this means for everyday life
Given these findings, families dealing with aging relatives or progressive cognitive conditions might want to consider discussing estate planning earlier rather than later, before capacity becomes questionable. If you have concerns about a family member’s ability to make or change a will, understanding that assessment standards vary by location and professional could help you seek appropriate evaluation. The research suggests that a comprehensive assessment should examine multiple cognitive domains—memory, comprehension, and decision-making ability—rather than relying on a single test or brief conversation. For those with fluctuating conditions like dementia, timing matters; capacity might vary day to day or even hour to hour. This review underscores why contested wills are so difficult to resolve: without standardized assessment protocols, different experts may reach different conclusions about the same person’s capacity. While you can’t control legal standards in your jurisdiction, awareness of these complexities might encourage more thorough documentation and professional assessment when estate planning involves someone with cognitive concerns.