It takes a particular kind of person to succeed in politics, but the psychological traits that make for leadership material could be more extreme than anybody ever realised.

A first-of-its-kind analysis ranking state-level estimates of psychopathy across the continental United States and the District of Columbia has found Washington DC harbours the highest concentration of psychopaths in the whole country.

The study, from economist Ryan Murphy at Southern Methodist University, builds off existing research that looked at how the so-called Big Five personality traits are spread across US states, based on personality samples of almost 1.6 million people.

These traits – extraversion, neuroticism, agreeableness, conscientiousness, and openness to experience – are used by researchers to help explain the psychological motivations behind people's behaviour, but some researchers think they also correspond to what makes people psychopaths.

While some definitions of psychopathy classify the condition as being binary – ie. you either have it, or you don't – other systems define it more like a spectrum, made up of variable levels of traits such as disinhibition, boldness, and meanness.

According to Murphy and other researchers though, these traits are already "nested" within the Big Five personality traits, which other researchers have already mapped out in the US.

"Boldness corresponds to low neuroticism and high extroversion, meanness corresponds to low agreeableness, and disinhibition corresponds to low conscientiousness," Murphy explains in his working paper, which hasn't yet been peer-reviewed.

"[Previous findings] can thereby be combined into a method of estimating the level of psychopathy for each US state."

Running that combination gives what Murphy admits is an "indirect methodology", but it nonetheless provides an inexpensive, back-of-the-envelope estimate of how psychopaths are distributed across the US – and one that's a heck of a lot simpler than conducting millions of individual psychopath tests, per assessments like the Hare Psychopathy Checklist.

When Murphy crunched the numbers, he found Connecticut was the most psychopathic state per capita, followed by California, New Jersey, and New York/Wyoming (which were equally tied in fourth place).

At the other end of the table, the five least psychopathic states were West Virginia, Vermont, Tennessee, North Carolina, and New Mexico.

But while Connecticut may have been the most psychopathic state, it wasn't actually the most psychopathic place, regionally speaking.

When Washington DC was included in the results alongside US states, it resulted in the single most extreme data point in the entire study – with a standardised psychopath score of 3.48 almost double Connecticut's 1.89.

While Murphy notes that Washington DC is a noisey and probably unreliable outlier in terms of the other data – since it's a highly populated urban area, notably different from many of the states looked at – it nonetheless might just add up.

"The presence of psychopaths in [the] District of Columbia is consistent with the conjecture … that psychopaths are likely to be effective in the political sphere," Murphy writes.

"The District of Columbia is measured to be far more psychopathic than any individual state in the country, a fact that can be readily explained either by its very high population density or by the type of person who may be drawn [to] a literal seat of power."

Things get even stranger when you consider that the study points out how previous research has found the most disproportionately psychopathic occupations are CEO, lawyer, media worker, salesperson, surgeon, journalist, police officer, clergy person, chef, and civil servant.

Politician isn't listed, but as Maureen Dowd at The New York Times observes, given what the research indicates about psychopaths being drawn to political power, at least one notable Washington DC inhabitant looks to be ticking a lot of boxes.

"If a chief executive, salesman, and media personality becomes a politician, he's hitting four of the highest-risk categories."

Hmmm.

The pre-print findings are available at the Social Science Research Network (SSRN).