“The U.S. economy bounced back with impressive resilience in the first quarter, startling all those who warned of a protracted post-Sept. 11 recession (the pessimists) or an unusually sluggish recovery (the optimists),” writes David Wessel in today’s Wall Street Journal.

“But the first quarter is history. What will the economy be like a year from now?”

“You could consult those same computer-aided forecasters who misjudged the economic impact of 9/11. Buoyed by the latest data, the middle-of-the-road forecast now sees the economy growing at an annual pace of around 3.5% over the next 12 months, and each revision is slightly rosier. Perhaps the forecasters will be right this time.”

“Or, you could acknowledge ignorance — yours, mine and the forecasters’ — and instead focus on what determines whether the economy soars or sinks. Another terrorist attack is an omnipresent risk. Today’s economic outlook is pleasant only because al Qaeda failed to strike successfully after Sept. 11.”

“What else could interrupt the economy’s welcome momentum? Make your own score card. Here are four hard-to-predict factors to watch because they’ll shape the U.S. economy over the next year or so.”

“Business investment. The vigor of the economy depends heavily on business executives’ willingness to invest, which ultimately turns on the mood in the nation’s boardrooms. Macroeconomic Advisers, a St. Louis forecasting firm, sees the economy growing at a 4% rate this year and next. The biggest single risk to that forecast, says the firm’s Joel Prakken, is its expectation that business capital spending, which dropped 6.4% last year, will grow 4.5% this year and 9.7% next, adjusted for inflation. One helpful development: the recent arrival of the new tax break to encourage investment.”

“Oil prices. They’re already rising. The benchmark price, which was below $20 a barrel earlier this year, is approaching $27 a barrel. As the global economy improves and OPEC tries to restrain production, oil prices may stay up. The economy can absorb that pressure. But a sharp and sustained spike in oil prices, the sort that might follow a U.S. invasion of Iraq, Arab oil producers’ reaction to U.S. support for Israel or a terrorist strike on a key oil-transit point could disrupt the nascent economic recovery.”

“Housing prices. When the stock market sank, the real-estate market didn’t. Rising home prices buoyed consumers’ spirits and, thanks to home-equity loans and refinancings, gave many of them money to keep spending right through the recession. Since New Year’s Day 2000, Americans’ stock portfolios have lost nearly $4 trillion, but their home equity has grown by $1.2 trillion. The government’s house price index, the best available measure, surged 9.2% in 2000 and 6.9% in 2001, though it slowed in the closing months of last year.”

“Greenspan’s future. A $10 trillion economy doesn’t turn on any one individual, but this one depends more on Alan Greenspan than on any other person. Global financial markets, politicians, corporate executives and ordinary Americans have confidence in his ability to steer the U.S. economy, particularly during times of crisis. The speed with which the Fed reacted in 2001, once it realized the economy was dead in the water, and its moves following Sept. 11 prevented panic.”