When we suppose that a segment X of the population is at high-risk for disorder Y, don't we assume that anyone carries the same psychophenotype, yet not in a statistically-significant degree?
When diagnosing Psychological/Psychiatric Disorders, psychologists would consider the extent of the patient's:
- Deviation from the norm;
- Danger to themselves and others;
- Dsyfunction, i.e. ability for the person to carry out tasks important for everyday functioning in an independent fashion.
The current paradigm uses a continuum model for disorders; how severe a psychologist would judge your disorder to be depends on the extent of the 4 D's. However, they're aren't weighted equally.
Deviation from the norm is, in fact, the factor with the least weight given when considering if someone has a mental disorder. What is abnormal for one society may be completely acceptable for another.
Instead, what is given more attention to is the extent of the distress and dsyfunction a person exhibits. The greater the distress or dsyfunction, the more serious your disorder will be placed within the continuum.
Danger is the iffy component, since usually the person with the mental disorder who will become the victim of exploitation, violence, and general hostility and fear. Because of this, it's usually only brought up when there is a clear and present danger to themselves or others.
"Are psychiatric disorders merely statistical deviations?" No. Psychiatric disorders are mostly defined by the client's subjective challenges in everyday situations.
When a client does not report to have any challenges in everyday situations, and reports to not feel that a condition is an issue, then no disorder will be diagnosed. If a client reports to have regular challenges in everyday situations, directly linked to a condition, then a disorder is likely to be diagnosed.
As such, disorders are indirectly diagnosed based on the norm. This means that if a society grows stricter expectations to individuals, then a growing proportion of the population will fail to accommodate these expectations, and this will theoretically result in more and more individuals being diagnosed with various disorders. This may very well be an explanation to why disorders are seemingly more common in wealthy cultures.