How do mental health professionals determine how to help the people they need to treat?  What kind of reasoning is required to determine that someone has an issue such as depression, anxiety, post-traumatic stress disorder, or the hundreds of others in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5)?  The manual’s listing of features suggests that assessment is just matching symptoms, for example seeing whether someone has 5 of the 9 symptoms that mark people as severely depressed.  But more complicated causal reasoning is needed to get a better understanding of people’s problems, in order to devise treatments that can help them. 

In a simpler world, psychotherapists (including psychiatrists and clinical psychologists) could assess people by straightforward deductive reasoning.  Suppose there were a rule that said:  If people have depressed mood most of the day and have markedly diminished interest or pleasure in life, then they are clinically depressed.  Then a therapist could infer from sad mood and disinterest that someone is depressed.  

Unfortunately, depression is much more complicated, and DSM requires that people only have at least one of depressed mood and diminished interest, along with at least four other symptoms such as significant weight loss or insomnia.  So, psychotherapeutic assessment is inductive rather than deductive, in order to distinguish between alternative explanations of people’s symptoms.   

The DSM’s menus of symptoms suggest that mental health professionals can just match the patterns of symptoms that people present with against the lists in the DSM.   Perhaps there are psychotherapists who rely on simple pattern matching, but there are many reasons why deeper forms of reasoning are required.

First, patient self-descriptions cannot always be taken at face value.   People are not always accurate at describing their moods and behaviors, because of lack of self-knowledge or negative emotions such as embarrassment and shame.  The therapist needs to make complex inferences about why patients are saying what they are saying, and about why they may be reluctant to reveal more.      

Second, there is much overlap in symptoms among different disorders, and people may suffer from multiple disorders at the same time such as depression AND anxiety.  The therapist can try to figure out how and why different problems are combined.

Third, listing symptoms says nothing about their causal origins.  Before the germ theory of disease was developed in the mid-1800s, medicine was largely symptom-based, for example when fever was considered a disease as well a symptom.  Since then, causal explanations have been developed for many kinds of disease such as cancer, nutritional deficiencies, and auto-immune disorders.  Eventually, there will be better understanding of how mechanisms break down to produce mental illnesses, but the authors of DSM-5 had to rely on lists of symptoms rather than causal understanding.   Nevertheless, the therapist can try to grasp why people are sad, disinterested, insomniac, agitated, fatigued, and so on.

Fourth, clinical assessment is not just a theoretical exercise, but has patient improvement as its goal.   For some patients, a quick symptom-based judgment of depression followed by efficient cognitive-behavioral therapy may work well.   But for others, treatment can benefit from dealing with underlying psychological and social causes. 

Accordingly, clinical assessment can require developing the kind of causal model shown in the figure, where the arrows indicate causality, and the dotted line indicates competing (but not contradictory) assessments.    Symptoms such as feeling sad and gaining weight can be explained by disorders such as depression or anxiety, which are in turn explained by factors such as having had an abusive parent and suffering from work stress.  Then diagnosis and subsequent treatment require building up a complex causal model of the patient, using it to infer the best explanation of the patient’s symptoms and to guide therapy

Paul Thagard
Source: Paul Thagard

 Psychotherapeutic sessions have many functions besides just determining the clients’ issues.  They can be used to monitor changes and adjust procedures, including assessing such aspects of the clients’ characteristics as duration, severity, and medication usage.  The psychotherapist also has to assess the capacity of clients to understand their own problems, their motivation to work collaboratively in treatment, which includes taking responsibility for their behaviors and the ability to develop a good working alliance with their therapist, a core mutual task.

Thanks to psychotherapist Laurette Larocque for helpful suggestions. 

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