Research led by Avshalom Caspi and Terrie Moffitt challenges the traditional way we think about mental health. For decades, science has often studied mental illnesses—like depression, anxiety, or ADHD—one at a time, searching for a specific cause for each one. However, this team’s latest work reveals that most mental disorders are more similar than they are distinct, and they often share the same underlying roots.

This research is built on an incredibly rigorous scientific foundation, drawing from three massive data sources: nationwide hospital records from Denmark, primary-care data from Norway, and the world-renowned Dunedin Study in New Zealand, which has followed a group of individuals for over 50 years.

The team’s findings highlight three key reasons why we should look at the "big picture" of mental health rather than focusing on single diagnoses:

• Partners and "Assortative Mating": The study found that people who experience mental health challenges tend to partner with others who also have a history of mental illness. Interestingly, they don’t always share the same diagnosis—someone with anxiety might partner with someone who has a history of substance use—which combines different risks within a family.
• A "Transdiagnostic" Family Risk: When mental illness runs in families, it doesn't just pass down one specific condition. Parents with a history of any disorder are more likely to have children who develop a wide range of different mental health challenges. This suggests that what is actually inherited is a general vulnerability to mental illness, rather than a specific "gene for depression" or "gene for ADHD".
• The Changing Course of a Lifetime: Over a person’s life, mental health is rarely static. The researchers found that most people who experience one disorder will likely experience others as they age. An individual might struggle with anxiety in their teens, depression in their 30s, and something else later on. The team uses a "deck of cards" analogy to explain this: as a person moves through life, different "cards" (disorders) may be dealt at different times, all coming from the same deck of underlying risk.

This general tendency to develop various forms of mental illness is what scientists call "p" (the "p" factor).

The takeaway for the public and for doctors is significant: treating a single symptom or diagnosis is often just seeing one piece of a much larger puzzle. By understanding a person's entire family and life history, clinicians can provide more holistic care that prepares patients for long-term mental health hygiene rather than just treating a current complaint. This shift in thinking could lead to more effective, tailored treatments that benefit families across generations.

Citation

Avshalom Caspi, Renate M. Houts, Anne Sofie Tegner Anker, Leah S. Richmond-Rakerd, Signe Hald Andersen, Reremoana Theodore, Richie Poulton, Terrie E. Moffitt, and Fartein Ask Torvik. "Why Psychopathology Research Should Avoid Studying One Mental Disorder at a Time: An Intergenerational and Developmental Evidence Base for Understanding “p”." Journal of Psychopathology and Clinical Science. https://doi.org/10.1037/abn0001042.