for (s in 1:S) { bio_sims <- rnorm(K, theta_new_samples_pop[s], sigma_bio_samples[s, 1]) weights_k <- numeric(K) for (k in 1:K) { weights_k[k] <- exp(log(dt((y_new_1 - bio_sims[k]) / sigma_X_samples[s, 1], df = df_samples[s, 1] ) / sigma_X_samples[s, 1]) + log(dt((y_new_2 - bio_sims[k]) / sigma_X_samples[s, 1], df = df_samples[s, 1] ) / sigma_X_samples[s, 1])) } weights_steady[s] <- mean(weights_k, na.rm = T) }

There is very little academic and statistical study of Wal-Mart’s impact on the health of its suppliers and virtually nothing in the last decade, when Wal-Mart’s size has increased by a factor of five. This while the retail industry has become much more concentrated. In large part, that’s because it’s nearly impossible to get meaningful data that would allow researchers to track the influence of Wal-Mart’s business on companies over time. You’d need cooperation from the vendor companies or Wal-Mart or both–and neither Wal-Mart nor its suppliers are interested in sharing such intimate detail.

Getting ready for Wal-Mart has been like putting Levi on the Atkins diet. It has helped everything–customer focus, inventory management, speed to market. It has even helped other retailers that buy Levis, because Wal-Mart has forced the company to replenish stores within two days instead of Levi’s previous five-day cycle.And so, Wal-Mart might rescue Levi Strauss. Except for one thing.Levi didn’t actually have any clothes it could sell at Wal-Mart. Everything was too expensive. It had to develop a fresh line for mass retailers: the Levi Strauss Signature brand, featuring Levi Strauss’s name on the back of the jeans.

“Everyone from the forklift driver on up to me, the CEO, knew we had to deliver [to Wal-Mart] on time. Not 10 minutes late. And not 45 minutes early, either,” says Robin Prever, who was CEO of Saratoga Beverage Group from 1992 to 2000, and made private-label water sold at Wal-Mart. “The message came through clearly: You have this 30-second delivery window. Either you’re there, or you’re out. With a customer like that, it changes your organization. For the better. It wakes everybody up. And all our customers benefited. We changed our whole approach to doing business.

Vlasic got to take it down to just over half a gallon of pickles, for $2.79. Not long after that, in January 2001, Vlasic filed for bankruptcy–although the gallon jar of pickles, everyone agrees, wasn’t a critical factor.

How can it be bad for things to come into the U.S. cheaply? How can it be bad to have a bargain at Wal-Mart?’ Sure, it’s held inflation down, and it’s great to have bargains,” says Dobbins. “But you can’t buy anything if you’re not employed. We are shopping ourselves out of jobs.

Wal-Mart, which in the late 1980s and early 1990s trumpeted its claim to “Buy American,” has doubled its imports from China in the past five years alone, buying some $12 billion in merchandise in 2002. That’s nearly 10% of all Chinese exports to the United States.

Wal-Mart no longer has any real rivals. It does more business than Target, Sears, Kmart, J.C. Penney, Safeway, and Kroger combined. “Clearly,” says Edward Fox, head of Southern Methodist University’s J.C. Penney Center for Retailing Excellence, “Wal-Mart is more powerful than any retailer has ever been.” It is, in fact, so big and so furtively powerful as to have become an entirely different order of corporate being.

The retailer has a clear policy for suppliers: On basic products that don’t change, the price Wal-Mart will pay, and will charge shoppers, must drop year after year. But what almost no one outside the world of Wal-Mart and its 21,000 suppliers knows is the high cost of those low prices