Elections are short and simple in most modern democracies. Voters usually pick only congressional candidates during a four- to six-week election season, and the winning party or parties then pick the head of state. Where presidential candidates run separately from congressional candidates, there is usually no lengthy nomination process, and a runoff may be required if no candidate wins a majority of the popular vote in the first round of voting.

But American elections are different.

Our presidential elections last roughly 10 months�from the first caucuses and primaries in Iowa and New Hampshire through the November election day. Public opinion can be volatile, especially during the early primaries, the national conventions and the fall debates. Parties and interest groups raise hundreds of millions of dollars to support their candidate.

Yet while American presidential elections are complex, they are by no means unpredictable. In modern elections, at least nine factors help predict the winner. How do these factors aid either George W. Bush or John Kerry this fall?

The economy, incumbency, party loyalty and voter turnout

The American economy usually tops the list as the most important influence in voting. When the economy fails to grow�or more rarely, when it shrinks�or when inflation or joblessness are high, incumbent presidents and their parties usually lose. While running against Jimmy Carter in 1980, former President Ronald Reagan popularized the term "misery index" and encouraged voters to ask whether they were better off than four years ago. Today's inflation rate at about 2 percent annually and unemployment under 6 percent�a "misery index" of 8 percent�would usually help an incumbent win re-election. Yet with the media's focus on the weak job growth, a stagnant stock market and jobs moving overseas, call this no net advantage to either Republicans or Democrats.

Beyond the economy, the advantages of incumbency usually help a sitting president. By dominating the news and handing out federal grants, a president can hold public attention without appearing to campaign. A large and experienced White House staff also helps to supplement the campaign. For 2004 call this a small net Republican advantage.

Party loyalty and turnout rates also influence presidential elections. Through the mid-1980s Democrats enjoyed a big advantage in party loyalty, although it did not guarantee that their nominees would win the presidency. Today the partisan balance between Republicans and Democrats is razor thin. Recent Gallup Polls put the split at 45.2 percent Democrats and 45.5 percent Republicans, with only 9 percent of Americans not leaning to either party. Since party identifiers vote overwhelmingly for their own party's nominee, neither Bush nor Kerry seems likely to pull out a landslide win. As a further twist, barely half of adult Americans vote in presidential elections at all, and both parties spend heavily getting their voters to the polls, especially in the 15-20 competitive states. Call this no net advantage.

The Electoral College, running mates and campaign finance

The Electoral College dictates that candidates pitch their campaigns in competitive states and ignore large but uncompetitive states like New York, California and Texas. The Electoral College virtually guarantees each major party candidate 150-200 electoral votes of the 270 needed to win. Unique among worldwide democracies, the Electoral College allows a popular vote loser to become an Electoral College winner. Since Democrats usually "waste" so many votes in California and New York, today's Electoral College has a small net Republican advantage.

Vice presidential candidates seldom rank high among voter concerns, although they do receive heavy media attention and occasionally help pick up a state. Neither Vice President Dick Cheney nor North Carolina Sen. John Edwards seems likely to add many votes nationwide or even an extra state to the ticket's Electoral College total. No net advantage.

Campaign finance laws are among the oddest features of American elections. Once nominated, a major party candidate is limited to $75 million in federal funds to run his fall campaign. This is dramatically inadequate for a two- to three-month nationwide effort. Consider that Mel Gibson's The Passion of the Christ grossed $76 million its first weekend or that this summer's sci-fi film, I Robot, grossed $95 million its first two weeks. Fortunately for both Kerry and Bush, their parties and interest groups supplement this figure with millions of additional dollars directed at likely supporters and swing voters. Campaign finance reformers notwithstanding, both candidates' supporters can be counted on to raise up to $200 million extra this year. No net advantage.

Up to a third of American voters explain their vote choice in terms of personal qualities, according to exit day polls.

Campaign staff, personal image and third-party candidates

Political scientists too often overlook the quality of a candidate's staff. Both the Kerry and Bush campaigns have been competently managed, so far avoiding any major gaffes. Even so, both campaigns have left questions about whether they can achieve a breakaway advantage. Why did the Democrats schedule their convention in Boston with a leadoff lineup of faded Democratic politicians? Why did the Republicans schedule their national convention in New York, a state they cannot win? No net advantage.

A candidate's personal image is the eighth influence on presidential elections. Up to a third of American voters explain their vote choice in terms of personal qualities, according to exit day polls. By mid-July, Gallup Polls put "caring about the needs of people like you" as John Kerry's strongest image (a net advantage of 6 percent). Being a "strong and decisive leader" and "not changing his positions on issues for political reasons" were George W. Bush's strongest personal traits (a 17 percent and 24 percent net advantage, respectively). Personal traits are especially important in a year where voters do not focus on a single most important issue. In mid-July Gallup Polls, for example, 28 percent of registered voters called the economy their most important concern, followed by Iraq (23 percent), terrorism (19 percent) and health care (16 percent). Abortion, gay marriage and gun control ranked further down. No net advantage.

Finally, in rare cases third-party candidates affect presidential elections. Seldom do they do so by winning large shares of votes, but often they can force major candidates to change their strategies or tip the balance in close states. Since Ross Perot's Reform Party has virtually disappeared and Ralph Nader has struggled to mount a campaign, count this as no net advantage.

Another close one?

This short review suggests two conclusions. First, no single factor like the fall debate performance or celebrity endorsements usually "decides" American presidential elections. Second, neither George W. Bush nor John Kerry goes into this fall's election with an overwhelming advantage.

The 2004 election may well be as close and competitive as the 2000 presidential election. There is also no guarantee that November's popular vote winner will also win enough Electoral College votes to take office as president in January 2005.

— Thomas R. Marshall