How Psychologists Capture the Complexities of Mental Illness

When it comes to understanding and treating mental illness, clinical psychologists must strike a balance between grouping people with shared characteristics together and recognizing people’s individual paths, circumstances, and needs. Below I’ve described some of the models that clinical psychologists use to reflect these complexities.

1) Biopsychosocial Model

Most modern psychologists understand that mental illness is the result of both nature and nurture. Accordingly, biopsychosocial models map out biological, psychological, and social risk factors for mental health outcomes and highlight potential intervention points. This model is so prominent that clinical psychology graduate programs require education in human development, individual differences, and biological, cognitive, affective, and social aspects of behavior, and you can’t become a licensed psychologist without passing a formal test on these topics. The idea is that mental health outcomes result from the interplay of biological, psychological, and sociocultural factors and that different people arrive at outcomes through different combinations of factors. Here’s a sample I constructed from some suicide risk factors:


2) Diathesis-Stress Model

People with identical genetics (i.e., monozygotic twins) and people with shared stressful events (e.g., witnessing the same violent act) can have different mental health outcomes. For example, many people with family histories of eating disorders will not develop eating disorders. Likewise, many people who have been bullied about their weight will not develop eating disorders. A diathesis-stress model of eating disorders explains this by saying that a person must have both a vulnerability (e.g., a genetic predisposition) and a significant stressor (e.g., weight-related bullying) to develop an eating disorder.


3) Multifinality and Equifinality

People who experience a similar event (e.g., trauma) can have disparate outcomes that depend on other factors (e.g., financial resources, societal views of survivors). This is called multifinality. Meanwhile, people with similar outcomes (e.g., posttraumatic stress disorder) can arrive there via distinct pathways (e.g., surviving sexual assault, a car accident, being the victim of gun violence). This is captured with the term equifinality.


4) Distal vs. Proximal Factors

Most research on mental illness focuses on a few risk factors per study. Organizing findings across studies can feel like fitting puzzle pieces together to create a holistic picture. One way to do this is by grouping risk factors in terms of how far in time (distal) and how close in time (proximal) they are to the onset of mental illness. For example, strategies for reducing distal risk factors for adult depression may include public policy efforts to prevent childhood maltreatmentincrease access to quality health care, and decrease discrimination. Meanwhile, therapy for individuals with depression may focus on more proximal factors (e.g., enhancing coping skills, increasing social support, behavioral activation).

distal proximal

5) Nomothetic vs. Idiographic

I highly recommend this article by Beltz, Wright, Sprague, and Molenaar (2016) for detailed definitions of these terms:nom idioFor example, imagine that a client gets diagnosed with obsessive-compulsive disorder (OCD). In order to figure out the best way to help, a therapist begins with nomothetic information (e.g., the diagnosis) to select a treatment. A randomized clinical trial suggests that a type of cognitive-behavioral therapy called exposure and response prevention (EX/RP) leads to significant improvement among 80% of people with OCD after 17 sessions. Based on available information, EX/RP is a good place to start. However, it’s possible that the client will be among the 20% of people who don’t respond to EX/RP. Therefore, therapists must also pay attention to idiographic information after initiating treatment (e.g., by regularly assessing the client’s OCD symptoms over time). If the client’s not responding to therapy, the idiographic data signal that the therapist must figure out why and make appropriate changes.


For more information on nomothetic and idiographic approaches, check out:

Clinical Practice as Natural Laboratory for Psychotherapy Research: A Guide to Case-Based Time-Series Analysis

Clinical Versus Actuarial Judgment

Single-Case Experimental Designs for the Evaluation of Treatments for Self-Injurious and Suicidal Behaviors

What Can the Clinician Do Well?

I’ve described frameworks that clinical psychologists use to understand people’s mental health needs at multiple levels while respecting their individuality. The dedicated people working hard to alleviate suffering in the face of these challenges give me hope for the future of the field.