Amity Shlaes explains for City Journal why popular economic metrics can prove misleading.

At least for now, most progressives acknowledge that markets and economic growth are necessary. But progressives in academia contend that growth has proved itself secondary to equality efforts—something to be exploited, rather than appreciated. Not just nationally, but worldwide, policymakers and the press regard the subordination of growth to equality to be a benign practice, as in the recent line in the Indian periodical Mint: a policy aimed at “reducing inequality need not hurt growth.”

The redistributionist impulse has brought to the fore metrics such as the Gini coefficient, named after the ur-redistributor, Corrado Gini, an Italian social scientist who developed an early statistical measure of income distribution a century ago. A society where a single plutocrat earns all the income ranks a pure “1” on the Gini scale; one in which all earnings are perfectly equally distributed, the old Scandinavian ideal, scores a “0” by the Gini test. …

… Through Gini’s lens, we now rank past eras. Decades in which policy endeavored or managed to even out and equalize earnings—the 1930s under Franklin Roosevelt, the 1960s under Lyndon Johnson—score high. Decades where policymakers focused on growth before equality, such as the 1920s, fare poorly. Decades about which social-justice advocates aren’t sure what to say—the 1970s, say—simply drop from the discussion. In the same hierarchy, federal debt moves down as a concern because austerity to reduce debt could hinder redistribution. Lately, advocates of economically progressive history have made taking any position other than theirs a dangerous practice. Academic culture longs to topple the idols of markets, just as it longs to topple statutes of Robert E. Lee.

But progressives have their metrics wrong and their story backward. The geeky Gini metric fails to capture the American economic dynamic: in our country, innovative bursts lead to great wealth, which then moves to the rest of the population. Equality campaigns don’t lead automatically to prosperity; instead, prosperity leads to a higher standard of living and, eventually, in democracies, to greater equality.