Personality & Individual Differences · Simplified

Where the Line Goes

People are spread along personality dimensions rather than sorted into kinds. Somewhere along the way somebody has to decide where a description becomes a clinical question.

What this is and is not. This page contains no diagnostic instrument and returns no diagnosis. It asks you nothing about yourself or about anybody you know, names nobody, names no diagnosis, and reproduces no criteria from any classification system. The four profiles are invented pairs of numbers on invented scales, and the phrase used throughout is that a profile falls above or below a line, which is a statement about the line. Personality difficulties are real, they cause real suffering, and nothing here makes light of that. What is being examined is the step from a continuous description to a category, and who takes it.

Step 1 of 2

First, a judgement

What most makes a personality pattern a clinical question rather than simply a personality?

Step 2 of 2

Four profiles, one line

Four invented profiles, each described by two numbers that are not calculated from each other: how far its traits sit from the average, and how much the pattern interferes with living. You control where the line falls and which of the two rules draws it. None of the four profiles changes at any point.

Key terms

Dimensional and categorical: Describing a profile by where it sits on continua, and sorting it into a class by applying a cut. The same numbers can be handled either way.
Trait extremity: How far from the average of a population a pattern sits. It is a statement about a distribution, not about difficulty.
Interference: How inflexible and persistent the pattern is and how much it gets in the way of work, relationships and daily life.
Prevalence: How many people fall above the line. When the underlying dimension is continuous, this is set by where the line goes.

On the same 0 to 100 scale as the profiles. Nothing in the data suggests a value; it is chosen.

Counting unusual features is how a great deal of classification has historically worked, so it is not a straw man.

Each marker is one invented profile, placed by how unusual its traits are and by how much the pattern interferes. The heavy line is the current cut, and the shaded region is the side that would be counted. The markers never move.


Profile	How unusual the traits are	How much it interferes	Which side of the line

What this shows

The cut is a decision, and it is not a small one

Key idea: Two of these four profiles change sides when the rule changes, and neither of them moved. One has traits a long way from the average and is managing perfectly well; the other has unremarkable traits and a great deal of difficulty. Which of them gets counted is decided entirely by whether the rule is about distance from the average or about interference, and that is the substantive question the word "disorder" is usually being asked to settle quietly. The second thing the controls show is that the number of people above the line is set by where the line goes: moving it across its range changes the share of a fictional population above it by more than twentyfold, with no person in that population changing. None of this makes the difficulties unreal. It means that a category imposed on a continuum inherits a decision, and that the honest thing is to say what the decision was and what it was for, rather than to treat the resulting count as something that was discovered.

Four invented profiles and two invented scales, chosen to make the argument legible. Real assessment does not consist of two numbers and a threshold; it involves history, context, corroboration and time, and clinicians are not unaware of any of this. Three cautions. That a boundary is a decision does not make what falls either side of it arbitrary or unreal, and it does not follow that categories are useless: they carry information about what has helped before, and they open doors to care that dimensions currently do not. Distress is deliberately not one of the two dimensions here, because it is a reason for help in its own right and can be present without interference or absent with it; folding it into either axis would have hidden that. And this page is not a position on any particular classification system, current or proposed. It is about what happens arithmetically when a continuum is cut, which is true of every cut on every continuum.

The longer version uses six dimensions rather than two, all of them separately settable, lets you build profiles of your own, and includes a worked pair with identical trait extremity and very different functioning. It is at Personality Disorder Continuum in the main collection.