A smooth-running event is not a matter of chance, Stephen Phillips finds. Behind the scenes, wily organisers have got preparation down to a fine art

AAAS staff were braced for a hefty turnout for palaeontologist Stephen Jay Gould's session at one of the association's annual meetings in the early Eighties. Gould, whose The Mismeasure of Man , debunking IQ testing, had just been published, was hot property. But nothing could prepare conference organisers for the scrum of spectators packing the room to hear the great man.

Spooked by the fire hazard the congested room posed, the hotel fire marshal relocated the session to a larger auditorium mid-stream. The loquacious Gould barely missed a beat, picking up where he left off in the new setting.

Conference organisers have to plan for every eventuality, but even so there can be problems.

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You can anticipate, for instance, that "Tissue engineering for the head and neck", one of the sessions at this year's conference, will have a niche audience. But others are harder to assess.

Leslie Warrick, AAAS meetings manager, says: "Guessing the size of the room is one of the biggest challenges. Everyone thinks their session is the most interesting, so you have to solicit opinions. Sometimes you guess right, other times wrong."

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In the wake of the recent landing of the European Space Agency's probe Huygens on Saturn's largest moon, Titan, the presentation from Cornell University's Steven Squyres, lead scientist on Nasa's Mars Rover Exploration Mission, is tipped to be this year's hot ticket, with a suitably capacious room reserved. But it's a lottery, Warrick concedes.

Selecting host cities is a similar minefield, says Jill Perla, senior manager, marketing and meetings operations. The conference doesn't "fit" into some cities, she explains.

Los Angeles is a dicey proposition - just too spread out, Perla says, while the conference would be dwarfed in Chicago's cavernous McCormack Center, another prospective venue. Meanwhile, New York is too pricey for many conference participants.

The AAAS tends to do better in second-tier US cities such as Seattle, San Francisco and Boston, which have a lively science and ÖйúAƬ infrastructure and educated populations.

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But there is such a thing as wearing out your welcome, Perla warns.

It is strict policy to rotate locations, never returning to the same city more than once every five years. "You don't want to saturate the market," she says.

Once the venue is fixed, Warrick "cases" the hotel and convention centre to ensure it fits the bill and starts planning the logistics.

To assist her, she wields a 5in-thick manual that documents every last detail of the conference, from coffee breaks to plenary lectures. She also hands a copy of the conference checklist to hotel staff to ensure they are on top of everything.

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As the event draws near, she conducts intensive meetings with caterers and lighting and signage contractors to ensure that everyone understands their tasks.

Perla and Warrick love their jobs, but there is a thankless side to them.

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"If you make a mistake, 1,000 people see it, (but) if everything goes smoothly, everyone assumes that's the way things are supposed to be," Perla says.