But then comes the Christmas season. The subways and buses get more crowded with tourists and shoppers, and instead of running into an even fifty people a day, the average Manhattanite now has close contact with, say, fifty-five people a day. That may not sound like much of a difference, but for our flu bug it is critical. All of a sudden, one out of every ten people with the virus will pass it on not just to one new person but to two. The thousand carriers run into fifty-five thousand people now, and at a two-per-cent infection rate that translates into eleven hundred new cases the following day. Some of those eleven hundred will also pass on the virus to more than one person, so that by Day Three there are twelve hundred and ten Manhattanites with the flu and by Day Four thirteen hundred and thirty-one, and by the end of the week there are nearly two thousand, and so on up, the figure getting higher every day, until Manhattan has a full-blown flu epidemic on its hands by Christmas Day.
In the language of epidemiologists, fifty is the "tipping point" in this epidemic, the point at which an ordinary and stable phenomenona low-level flu outbreakcan turn into a public-health crisis.
Malcolm Gladwell, "The Tipping Point," The New Yorker, June 3, 1996
The study also stated that the massive busing in Louisville and Nashville did not necessarily mean that it was beneficial educationally.
"What it does mean is that the countywide solution . . . has kept the proportion of black enrollees in the individual schools at a level below the 'tipping point,' thereby minimizing the outflow of white students," the report concluded.
The Associated Press, November 8, 1977
"The New York Times," Information Bank Abstracts, December 6, 1976
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