A documentary on a porn star who has had sex with 251 people in the space of 10 hours packed them in at the Sundance Film Festival, America's premier showcase for independent film.

Porn star Annabel Chong's story is a lurid tale

Sex : The Annabel Chong Story is just one of a number of lurid documentaries that emerged this year as the hot ticket at the festival.

Another was American Pimp which portrays the underworld life of pimps and whores.

Its first screening was a mob scene, reportedly so much so that many of the trendy festival attendees, including Ben Affleck, nearly got excluded.

Execution technologist

A whole slew of other documentaries were on view, some admittedly with less shocking subject matter, but this year at Sundance there was a preoccupation with chronicling the dark side of the American Dream.

Film maker Errol Morris' new work, which premiered at Sundance, is Mr Death: The Rise and Fall of Fred A Leuchter, Jr.

Its central character is an expert on Death Row equipment, a self-styled humanist and execution technologist, who also happens to be a Holocaust denier.

In years past Sundance has introduced such critically acclaimed movies as Sex, Lies and Videotape, Shine, and The Usual Suspects.

For the festival now to be bringing the shocking documentary to the fore is not an aberration, it's just part of a wider trend that's being expressed most vividly on American TV.

On the small screen the most popular new form of entertainment is the shockumentary.

What happens when good pets turn bad? Fox's latest shockumentary has the answer

It's a TV genre pioneered by the Murdoch owned Fox network with titles that include When Good Pets Go Bad, World's Scariest Police Chases, and the one that started it all, Alien Autopsy: Fact or Fiction?

The proliferation of TV shockumentaries is being driven by economics at a time when the big American broadcasting networks are facing declining audiences.

Defecating on her boss's chair

Shockumentaries can be made cheaply, and they bring in young males, a key demographic group favoured by American advertisers, so the profits are huge.

TV shockumentaries are, for the most part, wretched and pathetic, although on first viewing often appear benign.

One example is Busted on the Job, which included scenes of a secretary, presumably caught on a surveillance camera, defecating on her boss's chair.

That's just a mild example which may sound funny at first, but it is creating entertainment based on the act of an extremely disturbed individual.

Realm of snuff movies

Many shockumentaries are far worse, with violence that moves into the realm of the snuff film.

When it comes to the upmarket shockumentaries that were screened at Sundance it's debatable whether these are truly artistic endeavours.

Gough Lewis, who made the Annabel Chong documentary, couldn't explain at a post-screening question and answer session why he'd allowed Chong to mutilate herself during filming - and then included the scene in his film.

Errol Morris has a strong track record and his Mr Death may be redeeming if it succeeds in its mission to understand humanity's capacity for evil.

Morris is probably the exception, rather than the rule, because documentaries with shocking subject matter often do no more than just pander to voyeuristic thrill seekers.

Cheating spouses caught on tape

Shockumentaries will spread because, as Sundance suggests, independent film makers definitely seem more interested than ever in documenting the pathology of bizarre American subcultures.

On American TV the prognosis is bleak, because the shockumentary form pioneered by Fox is now being adopted at the other three big networks.

In February network TV will broadcast a record number of these new shockumentaries.

Viewers can look forward to Cheating Spouses: Caught on Tape.

But in a moment of rare sanity network executives decided that a proposed show, Prisoners Out of Control, was too violent, so thankfully we've been spared, but probably not for long.

A well-known BBC entertainment correspondent, Tom has lived in New York and travelled extensively in the US for the past 20 years.