A treatment plan should be based on the best science available. This means that the therapist must be well-informed regarding recent scientific findings. The clinical hermeneutics error refers to the therapist losing track of the actual degree of pathology due to adopting the patient’s perspective. This means that high-level depth of processing or interpreting and explaining the behaviour leads to a loss of normative judgement.

The Neo-Kraepelinian diagnostic rubrics consist of ascertainment of facts to determine the presence or absence of relatively explicit diagnostic criteria (1), the making of differential and multi-axis diagnoses using the DSM (2) and the differential selection of treatment guided by differential diagnosis (3).

Diagnosis in the current practice misses the point that symptoms of presenting complaints and targets of treatment plan may be manifestations of personality traits. The features the diagnostician focuses on may be consequences of extreme levels of personality traits (1), problematic configurations of trait levels (2) or extreme adaptations to personality traits (3). A high degree of comorbidity may be the result of manifestations of the same few maladaptive personality traits (e.g. negative emotionality) which are interpreted as symptoms.

Personality traits influence how individuals interpret and construe life events. Science does not fully support the claim that major mental disorders are separate from personality. Constructive realism makes several statements:

1. Personality traits are real
   A trait refers to a psychological structure underlying a relatively enduring behavioural disposition.
2. Traits are separate from constructs and measures
   Constructs refer to elements in psychologists’ theories of traits. Traits become known through their behavioural implications but the manifest behaviours are not the traits.
3. Traits exist in individuals but lead to population concepts
   The different trait levels lead to trait dimensions which leads to population concepts (e.g. height in individuals leads to tallness as a concept in the population).

Trait levels refer to an individual’s specific dispositions. There are major replicable trait dimensions and they are organized hierarchically. There are three trait dimensions:

1. Extraversion
   This is an aspect of the broader dimension of positive emotionality (PE).
2. Neuroticism
   This is an aspect of the broader dimension of negative emotionality (NE).
3. Constraint
   This is related to reversed psychoticism and reversed sensation seeking.

Environmental effects consist of shared environmental factors and unshared environmental factors. Treatment planners should know about four things:

1. Heritability of personality traits
   This is the proportion of variance in a trait that is attributable to genetic influences. It is a population concept.
2. Initial findings on the source of personality trait stability
   A lot of stability of personality traits stems from genetic factors whereas change arises primarily from unshared environmental factors. Individuals with certain genotypes select environments that provide stability for their personality traits.
3. Gene-environment correlations
   It is through the agency of the person that environments are selected or created that are consonant with the genotype. It refers to the tendency of people to seek and create trait-relevant environments. This leads to personality stability. Passive gene-environment correlations results when parents provide both genes and environmental influences that contribute to the development of a characteristic in their children. Reactive gene-environment correlations occur when other individuals respond to behaviour produced by the individual’s genotype in characteristic ways.
4. Unexpected weakness of shared family influence in shaping personality traits
   The role of shared environmental influences on most personality traits in adulthood is negligible. Common environmental experiences do not contribute substantially to personality resemblance. The average expectable environments (i.e. not extreme environments) do not strongly promote personality similarity of family members.

Passive gene-environment correlations are substantial early in life and decline shortly thereafter. Reactive gene-environment correlation effects increase from childhood to adulthood.  

The principle of equipotentiality states that there are many potential life adaptations for any level of an individual difference. Markedly different life adaptations can reflect the same or similar underlying personality dispositions.

Basic tendencies refer to underlying dispositions. Characteristic adaptations refer to concrete habits, attitudes, roles, relationships and goals that result from the interaction of basic tendencies with the shaping forces of the social environment. For any level of basic tendency, there are many potential characteristic adaptations.

Adaptation includes coping with external circumstances and adaptation to one’s basic tendencies. People can have similar personality characteristics but express them in different ways (e.g. criminals and firefighters have similar scores in sensation seeking). The characteristic adaptation differs.

Dispositional measures may only show moderate correlations with diagnostic categories because diagnostic categories are complex descriptions that mix basic tendencies and characteristic adaptations.

Using personality trait assessment in clinical assessment has four benefits:

1. Knowing where change is possible
   Personality assessment contributes to treatment planning by helping to decide if problems are intimately linked with a person’s broad personality dispositions or whether they are more circumscribed. Assessment allows the clinician to determine where the problem stands on the simple-complex continuum. Personality assessment allows treatment to focus on characteristic adaptations rather than basic tendencies. Personality assessment could also remind the treatment planner that new characteristic adaptations should be construed with sensitivity to a client’s basic tendencies.
2. Realistic expectations
   Individual differences science (i.e. personality assessment) can provide the client with realistic expectations about therapy.
3. Matching treatment to personality
   A useful strategy for keeping a client interested and engaged with the therapy is to match the treatment to the personality of the client.
4. Growing a self
   Personality assessment, in combination with therapy, can lead to an increase in self-knowledge. This provides the client with more resources, options and capacities. Test feedback presented in a way that promotes the growth of self can reduce symptom distress.

 Simple problems involve situationally specific and transitory habits that are primarily products of current environmental contingencies (e.g. phobia of dogs). Complex problems involve cross-situationally pervasive signs and symptoms reflecting long-term patterns of adjustment. Complex problems can be seen as consequences of enduring personality traits. It is possible that basic tendencies are not influenced by shared family environment but characteristic adaptations are.