The Machine in the Market: Data Briefing

On the last Friday of July, Korea's stock market rose 17.9 percent, the largest one-day gain in its history, and the up-day, in our view, is the stranger fact, stranger than the crash that preceded it. In six weeks, the year's best-performing major market fell nearly 44 percent from its intraday peak, took the first consecutive-day trading halts its main board has ever needed, and produced an estimated $38.7 billion of household losses; the same week in New York, a fund still up roughly 80 percent on the year by its own account sold $16 billion of positions in one pre-open trade after margin calls, as widely reported.

None of the machinery behind those prints is uniquely Korean. Versions of it trade in our market every afternoon, roughly four times larger than in January, clustered around the ten names that are about 40 percent of your index fund. There are two honest readings of July. In one, Korea was an anomaly: leverage packed into two stocks with no American parallel, in a market a fraction of our depth, while the S&P 500 set a record the same week. In the other, Korea was a preview at small scale. What follows: the week reconstructed on the tape, the wrapper arithmetic, who paid whom, four decades of rhymes, and the dials we watch.