Over the weekend, Brendan Nelson drew on his medical past to play psychologist. In an interview with The Sydney Morning Herald, the outgoing Liberal MP and former Opposition leader diagnosed Malcolm Turnbull with narcissistic personality disorder.

On Sunday, Liberal frontbencher Tony Abbott also weighed into a little pop psychology, suggesting that it was PM Kevin Rudd, not Turnbull, who has narcissistic personality disorder.

So what is narcissistic personality disorder? And does Malcolm Turnbull have it? Crikey asked personality disorder expert Professor Henry Jackson from the University of Melbourne’s Department of Behavioural Science to shed some light.

According to Professor Jackson, narcissistic personality disorder is one of the 10 types of personality disorders outlined in the Diagnostic and Statistical Manual of Mental Disorders. The disorder is “characterised by patterns of grandiosity, a need for admiration, and most importantly, a lack of empathy for others,” said Professor Jackson.

“These people are pretty entitled and pretty exploitative of others,” said Jackson. “They can also be quite envious of others.”

Narcissistic personality disorder is a “disorder of self not a disorder of other” and these people “don’t give a damn about others,” said Jackson. This can mean that when the person affected by the disorder is disappointed by the people they require admiration from, they can turn quite nasty.

People affected by narcissistic personality disorder come from all walks of life, says Professor Jackson, and personality disorders such as this generally develop during childhood and over a period of time.

It is unclear, however, how many Australians are affected by this disorder as only limited studies have been carried out on specific populations. Professor Jackson estimates that between one and two per cent of the population may be affected.

People suffering from narcissistic personality disorder are unlikely to present to mental health professionals for treatment, says Professor Jackson, unless they experience a depressive episode following some form of loss in their lives, such as losing a position of power or going through a divorce. It makes sense that people suffering from this disorder are predisposed to depression given their sense of bravado and external self esteem.

When asked, Professor Jackson declined to comment on whether Turnbull could be categorised as having narcissistic personality disorder. From the information provided by Professor Jackson, it appears that Nelson’s diagnosis of Turnbull may be unfair, and only vaguely true at best.

Does Turnbull exhibit patterns of grandiosity? In Febuary this year, Labor MP Lindsay Tanner spoke of Turnbull’s “breathtaking arrogance” with regard to blocking Government legislation in the Senate. SMH columnist Annabel Crabb likened Turnbull to a chest-beating Tarzan “more comfortable with grand gestures” than the realities of political compromise.

A need for admiration? Sure. Most politicians and people in public life do. According to Abbott, “no one goes into politics without a pretty solid ego”.

High external self-esteem? As a former high-flying lawyer and now Leader of the Opposition of the nation’s federal parliament, it would be a pretty safe bet to say that Turnbull’s self esteem is quite healthy.

In 2000, author turned spinmeister to Turnbull, Mark Wesfield, wrote in his book The Gatekeepers:

Perhaps more than any person in Australian corporate circles, Malcolm Turnbull’s name inevitably provokes reaction. He can be courteous, charming and flattering one minute, and bursting with dark volcanic rage the next, depending on whether or not he is getting his way in negotiations.

But is Turnbull exploitative of others? Does he not give a damn about anyone else?

The answers to these questions might depend on what side of the political fence you sit on.

Perhaps the Liberal party’s recent romance with psychology might be more important for what it says about Nelson’s bitterness in leaving politics, than Turnbull’s personality.