FYI: Why will everybody be paying so much attention to New Hampshire, in the US, on Tuesday?

It's a peculiar feature of the United States electoral system that a state ranking near the bottom of the tables in terms of population, area and diversity has the biggest influence on the country's presidential contest. Small, largely rural and sedate, New Hampshire spends most of its time far from the spotlight. But on Tuesday, when its residents queue up to make their picks for the Democratic and Republican presidential candidates, it will be the focal point of a media frenzy.

New Hampshire's contest isn't even the first major event on the electoral calendar - it's preceded by the Iowa caucus, which took place last week. But in terms of visibility and sheer clout, the state's vote is unrivalled and it receives a disproportionate share of campaign face time and funding - as demonstrated by Rudy Giuliani's decision to spend US$2 million on advertising in a place where the population barely exceeds 1 million.

The stage for this anomaly was set in 1952 when, in a pair of major upsets, Republican Dwight Eisenhower defeated Robert Taft and the incumbent president, Harry S. Truman, lost out to fellow Democrat Estes Kefauver. Humiliated, Truman dropped out of the race and Eisenhower went on to win the presidential election, establishing New Hampshire's reputation as a predictor of national trends.

Indeed, every US president since has carried the crucial New Hampshire poll, with the notable exceptions of Bill Clinton, who was defeated in 1992 by then front-runner Paul Tsongas, and in 2000, George W. Bush, who received 30 per cent of the votes compared to John McCain's 49 per cent. This has created what's known to political scientists as the 'bandwagon effect', in which voters (and wallets) across the US rally behind candidates who do well in New Hampshire, while anyone who fails to inspire there can probably kiss their presidential ambitions goodbye.

In 1977, New Hampshire cemented its status by enacting a law that required its primary to be the nation's first. Inevitably there have been some complaints about the sway a wealthy, overwhelmingly white enclave has on US politics. In a bid to raise their profiles, faster-growing states with larger and more representative populations, such as Florida and Michigan, have been pushing to hold their primaries earlier in the year, leading to a massive crunch in February-March that forces presidential hopefuls to jump frantically from state to state to boost their appeal with voters. Some see it as only a matter of time before another state unseats New Hampshire as the presidential campaign's starting gun.

Conscious of the difficulties of the primary process, a few politicians and academics have put forward possible reforms, such as grouping the states into geographical regions and rotating which group gets to go first.