5.1.1 - Defining mental disorder

Deviance and context

Deviance means departing from an expected pattern, but the expectation must be made explicit before the departure can be interpreted.

Statistical deviance concerns rarity. A score far from the usual range on a measure may be unusual. Social deviance concerns a norm: an expectation about behaviour within a setting. Speaking loudly in a quiet ceremony might violate that setting's norm even if loud speech is common elsewhere. These are different meanings; rarity does not necessarily involve disapproval.

Deviance can alert a practitioner to an experience that deserves investigation. It can also be operationalised: a researcher can specify the behaviour or measurement counted as unusual. This makes a judgement clearer than simply saying that a person seems different.

The limitation is that unusual does not mean disordered. Exceptional memory is rare but can be beneficial. A political dissenter may violate a social expectation without having a mental disorder. Norms also change across time, cultures and situations. If a dominant group treats its own customs as universal, a deviance definition can pathologise difference. The relevant question is therefore which norm is being used and whether the departure indicates a clinically meaningful problem.

Dysfunction and impairment

Dysfunction directs attention to whether a pattern interferes with the person's ability to carry out important everyday activities.

For example, a persistent fear that prevents someone from leaving home may interfere with attending classes and buying food. This example links an experience to its effect; merely reporting fear does not show dysfunction. Practitioners consider how severe and persistent the interference is, how the person functioned previously, and what support or opportunities are available.

This approach is useful because it focuses on consequences for the individual rather than on whether observers approve of them. It can help identify a need for support even when the behaviour is not statistically rare. A widely experienced problem can still seriously interfere with life.

However, functioning is not a simple pass/fail test. A person may maintain work while struggling in other areas, or receive support that masks difficulties. Conversely, someone may be unable to work because no suitable job is available, because of a physical illness, or because they face discrimination. Inability to meet a social expectation is not automatically psychological dysfunction. Assessment must separate the person's difficulties from barriers in their circumstances.

Distress and subjective experience

Distress includes the person's own suffering, which an observer may not be able to infer from outward behaviour.