Big questions and big numbers examines economic models:
Both kinds of model share a debt to Leon Walras, a 19th-century French economist. Walras was adamant that one could not explain anything in an economy until one had explained everything. Each market — for goods, labour and capital — was connected to every other, however remotely. This interdependence is apparent whenever faster car sales in Texas result in an increase in grocery shopping in Detroit, the home of America’s “big three” carmakers. Or when steep prices for oil lead, curiously enough, to lower American interest rates, because the money the Saudis and the Russians make from crude is spent on American Treasury bonds. This fundamental insight moved one economist to quote the poetry of Francis Thompson: “Thou canst not stir a flower/Without troubling of a star.”Such thinking now comes naturally to economists. But it still escapes many politicians, who blindly uproot flowers, ignorant of the celestial commotion that may ensue. They slap tariffs on steel imports, for example, to save jobs in Pittsburgh, only to find this costs more jobs in the domestic industries that use the metal. Or they help to keep zombie companies alive — rolling over their loans, and preserving their employees on the payroll — only to discover they have starved new firms of manpower and credit. Big models, which span all the markets in an economy, can make policymakers think twice about the knock-on effects of their decisions.
Tyler Cowen cites this excerpt:
But how plausible were the numbers? Twelve years on, economists have shown little inclination to go back and check. One exception is Timothy Kehoe, an economist at the University of Minnesota. In a paper published last year, he argued that the models “drastically underestimated” NAFTA’s impact on trade flows (if not on jobs). The modellers assumed the trade pact would allow people to buy more of the goods for which they had already shown some appetite. In fact, the agreement set off an explosion in the exports of many products Mexico had scarcely traded before. Cars, for example, amounted to less than 1% of Mexico’s exports to Canada before the agreement. By 1999, however, they accounted for more than 15%. The only comfort economists can draw from their efforts, Mr Kehoe writes, is that their predictions fared better than Mr Perot’s. A low bar indeed.