Nate Silver 2012, The Signal and the Noise:
# ch7
On October 11, a report surfaced from Pittsburgh that three senior citizens had died shortly after receiving their flu shots; so had two elderly persons in Oklahoma City; so had another in Fort Lauderdale.18 There was no evidence that any of the deaths were linked to the vaccinations-elderly people die every day, after all.19 But between the anxiety about the government's vaccination program and the media's dubious understanding of statistics,20 every death of someone who'd gotten a flu shot become a cause for alarm. Even Walter Cronkite, the most trusted man in America-who had broken from his trademark austerity to admonish the media for its sensational handling of the story-could not calm the public down. Pittsburgh and many other cities shuttered their clinics.21
By late fall, another problem had emerged, this one far more serious. About five hundred patients, after receiving their shots, had begun to exhibit the symptoms of a rare neurological condition known as Guillain-Barré syndrome, an autoimmune disorder that can cause paralysis. This time, the statistical evidence was far more convincing: the usual incidence of Guillain-Barré in the general population is only about one case per million persons.22 In contrast, the rate in the vaccinated population had been ten times that-five hundred cases out of the roughly fifty million people who had been administered the vaccine. Although scientists weren't positive why the vaccines were causing Guillain-Barré, manufacturing defects triggered by the rush production schedule were a plausible culprit,23 and the consensus of the medical community24 was that the vaccine program should be shut down for good, which the government finally did on December 16.
In the end, the outbreak of H1N1 at Fort Dix had been completely isolated; there was never another confirmed case anywhere in the country.25 Meanwhile, flu deaths from the ordinary A/Victoria strain were slightly below average in the winter of 1976-77.26 It had been much ado about nothing.
The swine flu fiasco-as it was soon dubbed-was a disaster on every level for President Ford, who lost his bid for another term to the Democrat Jimmy Carter that November.27 The drug makers had been absolved of any legal responsibility, leaving more than $2.6 billion in liability claims28 against the United States government. It seemed like every local paper had run a story about the poor waitress or schoolteacher who had done her duty and gotten the vaccine, only to have contracted Guillain-Barré. Within a couple of years, the number of Americans willing to take flu shots dwindled to only about one million,29 potentially putting the nation in grave danger had a severe strain hit in 1978 or 1979.30
Ford's handling of H1N1 was irresponsible on a number of levels. By invoking the likelihood of a 1918-type pandemic, he had gone against the advice of medical experts, who believed at the time that the chance of such a worst-case outcome was no higher than 35 percent and perhaps as low as 2 percent.31
The controversial 1968 book The Population Bomb, by the Stanford biologist Paul R. Ehrlich and his wife, Anne Ehrlich, made the opposite mistake, quite wrongly predicting that hundreds of millions of people would die from starvation in the 1970s.49 The reasons for this failure of prediction were myriad, including the Ehrlichs' tendency to focus on doomsday scenarios to draw attention to their cause. But one major problem was that they had assumed the record-high fertility rates in the free-love era of the 1960s would continue on indefinitely, meaning that there would be more and more hungry mouths to feed.* "When I wrote The Population Bomb I thought our interests in sex and children were so strong that it would be hard to change family size," Paul Ehrlich told me in a brief interview. "We found out that if you treat women decently and give them job opportunities, the fertility rate goes down." Other scholars who had not made such simplistic assumptions realized this at the time; population projections issued by the United Nations in the 1960s and 1970s generally did a good job of predicting what the population would look like thirty or forty years later.50
Extrapolation tends to cause its greatest problems in fields-including population growth and disease-where the quantity that you want to study is growing exponentially. In the early 1980s, the cumulative number of AIDS cases diagnosed in the United States was increasing in this exponential fashion:51 there were 99 cases through 1980, then 434 through 1981, and eventually 11,148 through 1984. You can put these figures into a chart, as some scholars did at the time,52 and seek to extrapolate the pattern forward. Doing so would have yielded a prediction that the number of AIDS cases diagnosed in the United States would rise to about 270,000 by 1995. This would not have been a very good prediction; unfortunately it was too low. The actual number of AIDS cases was about 560,000 by 1995, more than twice as high.
Perhaps the bigger problem from a statistical standpoint, however, is that precise predictions aren't really possible to begin with when you are extrapolating on an exponential scale. A properly applied version53 of this method, which accounted for its margin of error, would have implied that there could be as few as 35,000 AIDS cases through 1995 or as many as 1.8 million. That's much too broad a range to provide for much in the way of predictive insight. [53. The version I applied here was to log-transform both the year variable and the AIDS-cases variable, then calculate the exponent via regression analysis. The 95 percent confidence interval on the exponent ran from about 2.2 to 3.7 by this method, with a most likely value of about 2.9. When applied ten years into the future, those relatively modest-seeming differences turn into an exceptionally broad range of possible outcomes.]
There are two major north-to-south routes through Manhattan: the West Side Highway, which borders the Hudson River, and the FDR Drive, which is on Manhattan's east side. Depending on her destination, a driver may not strongly prefer either thoroughfare. However, her GPS system will tell her which one to take, depending on which has less traffic-it is predicting which route will make for the shorter commute. The problem comes when a lot of other drivers are using the same navigation systems-all of a sudden, the route will be flooded with traffic and the "faster" route will turn out to be the slower one. There is already some theoretical66 and empirical67 evidence that this has become a problem on certain commonly used routes in New York, Boston, and London, and that these systems can sometimes be counterproductive.
The late 1990s and early 2000s were accompanied by a marked rise in unprotected sex in San Francisco's gay community,70 which had been devastated by the HIV/AIDS pandemic two decades earlier. Some researchers blamed this on increasing rates of drug use, particularly crystal methamphetamine, which is often associated with riskier sexual behavior. Others cited the increasing effectiveness of antiretroviral therapy-cocktails of medicine that can extend the lives of HIV-positive patients for years or decades: gay men no longer saw an HIV diagnosis as a death sentence. Yet other theories focused on generational patterns-the San Francisco of the 1980s, when the AIDS epidemic was at its peak, was starting to feel like ancient history to a younger generation of gay men.71
The one thing the experts agreed on was that as unprotected sex increased, HIV infection rates were liable to do so as well.72
But that did not happen. Other STDs did increase: the number of new syphilis diagnoses among men who have sex with men (MSM)73-which had been virtually eradicated from San Francisco in the 1990s-rose substantially, to 502 cases in 2004 from 9 in 1998.74 Rates of gonorrhea also increased. Paradoxically, however, the number of new HIV cases did not rise. In 2004, when syphilis reached its highest level in years, the number of HIV diagnoses fell to their lowest figure since the start of the AIDS epidemic. This made very little sense to researchers; syphilis and HIV are normally strongly correlated statistically, and they also have a causal relationship, since having one disease can make you more vulnerable to acquiring the other one.75
The solution to the paradox, it now appears, is that gay men had become increasingly effective at "serosorting"-that is, they were choosing sex partners with the same HIV status that they had. How they were able to accomplish this is a subject of some debate, but it has been documented by detailed behavioral studies in San Francisco,76 Sydney,77 London, and other cities with large gay populations. It may be that public health campaigns-some of which, wary of "condom fatigue," instead focused on the notion of "negotiated safety"-were having some positive effect. It may be that the Internet, which to some extent has displaced the gay bar as the preferred place to pick up a sex partner, has different norms for disclosure: many men list their HIV status in their profiles, and it may be easier to ask tough questions (and to get honest responses) from the privacy of one's home than in the din of the dance hall.78
# ch7
On October 11, a report surfaced from Pittsburgh that three senior citizens had died shortly after receiving their flu shots; so had two elderly persons in Oklahoma City; so had another in Fort Lauderdale.18 There was no evidence that any of the deaths were linked to the vaccinations-elderly people die every day, after all.19 But between the anxiety about the government's vaccination program and the media's dubious understanding of statistics,20 every death of someone who'd gotten a flu shot become a cause for alarm. Even Walter Cronkite, the most trusted man in America-who had broken from his trademark austerity to admonish the media for its sensational handling of the story-could not calm the public down. Pittsburgh and many other cities shuttered their clinics.21
By late fall, another problem had emerged, this one far more serious. About five hundred patients, after receiving their shots, had begun to exhibit the symptoms of a rare neurological condition known as Guillain-Barré syndrome, an autoimmune disorder that can cause paralysis. This time, the statistical evidence was far more convincing: the usual incidence of Guillain-Barré in the general population is only about one case per million persons.22 In contrast, the rate in the vaccinated population had been ten times that-five hundred cases out of the roughly fifty million people who had been administered the vaccine. Although scientists weren't positive why the vaccines were causing Guillain-Barré, manufacturing defects triggered by the rush production schedule were a plausible culprit,23 and the consensus of the medical community24 was that the vaccine program should be shut down for good, which the government finally did on December 16.
In the end, the outbreak of H1N1 at Fort Dix had been completely isolated; there was never another confirmed case anywhere in the country.25 Meanwhile, flu deaths from the ordinary A/Victoria strain were slightly below average in the winter of 1976-77.26 It had been much ado about nothing.
The swine flu fiasco-as it was soon dubbed-was a disaster on every level for President Ford, who lost his bid for another term to the Democrat Jimmy Carter that November.27 The drug makers had been absolved of any legal responsibility, leaving more than $2.6 billion in liability claims28 against the United States government. It seemed like every local paper had run a story about the poor waitress or schoolteacher who had done her duty and gotten the vaccine, only to have contracted Guillain-Barré. Within a couple of years, the number of Americans willing to take flu shots dwindled to only about one million,29 potentially putting the nation in grave danger had a severe strain hit in 1978 or 1979.30
Ford's handling of H1N1 was irresponsible on a number of levels. By invoking the likelihood of a 1918-type pandemic, he had gone against the advice of medical experts, who believed at the time that the chance of such a worst-case outcome was no higher than 35 percent and perhaps as low as 2 percent.31
The controversial 1968 book The Population Bomb, by the Stanford biologist Paul R. Ehrlich and his wife, Anne Ehrlich, made the opposite mistake, quite wrongly predicting that hundreds of millions of people would die from starvation in the 1970s.49 The reasons for this failure of prediction were myriad, including the Ehrlichs' tendency to focus on doomsday scenarios to draw attention to their cause. But one major problem was that they had assumed the record-high fertility rates in the free-love era of the 1960s would continue on indefinitely, meaning that there would be more and more hungry mouths to feed.* "When I wrote The Population Bomb I thought our interests in sex and children were so strong that it would be hard to change family size," Paul Ehrlich told me in a brief interview. "We found out that if you treat women decently and give them job opportunities, the fertility rate goes down." Other scholars who had not made such simplistic assumptions realized this at the time; population projections issued by the United Nations in the 1960s and 1970s generally did a good job of predicting what the population would look like thirty or forty years later.50
Extrapolation tends to cause its greatest problems in fields-including population growth and disease-where the quantity that you want to study is growing exponentially. In the early 1980s, the cumulative number of AIDS cases diagnosed in the United States was increasing in this exponential fashion:51 there were 99 cases through 1980, then 434 through 1981, and eventually 11,148 through 1984. You can put these figures into a chart, as some scholars did at the time,52 and seek to extrapolate the pattern forward. Doing so would have yielded a prediction that the number of AIDS cases diagnosed in the United States would rise to about 270,000 by 1995. This would not have been a very good prediction; unfortunately it was too low. The actual number of AIDS cases was about 560,000 by 1995, more than twice as high.
Perhaps the bigger problem from a statistical standpoint, however, is that precise predictions aren't really possible to begin with when you are extrapolating on an exponential scale. A properly applied version53 of this method, which accounted for its margin of error, would have implied that there could be as few as 35,000 AIDS cases through 1995 or as many as 1.8 million. That's much too broad a range to provide for much in the way of predictive insight. [53. The version I applied here was to log-transform both the year variable and the AIDS-cases variable, then calculate the exponent via regression analysis. The 95 percent confidence interval on the exponent ran from about 2.2 to 3.7 by this method, with a most likely value of about 2.9. When applied ten years into the future, those relatively modest-seeming differences turn into an exceptionally broad range of possible outcomes.]
There are two major north-to-south routes through Manhattan: the West Side Highway, which borders the Hudson River, and the FDR Drive, which is on Manhattan's east side. Depending on her destination, a driver may not strongly prefer either thoroughfare. However, her GPS system will tell her which one to take, depending on which has less traffic-it is predicting which route will make for the shorter commute. The problem comes when a lot of other drivers are using the same navigation systems-all of a sudden, the route will be flooded with traffic and the "faster" route will turn out to be the slower one. There is already some theoretical66 and empirical67 evidence that this has become a problem on certain commonly used routes in New York, Boston, and London, and that these systems can sometimes be counterproductive.
The late 1990s and early 2000s were accompanied by a marked rise in unprotected sex in San Francisco's gay community,70 which had been devastated by the HIV/AIDS pandemic two decades earlier. Some researchers blamed this on increasing rates of drug use, particularly crystal methamphetamine, which is often associated with riskier sexual behavior. Others cited the increasing effectiveness of antiretroviral therapy-cocktails of medicine that can extend the lives of HIV-positive patients for years or decades: gay men no longer saw an HIV diagnosis as a death sentence. Yet other theories focused on generational patterns-the San Francisco of the 1980s, when the AIDS epidemic was at its peak, was starting to feel like ancient history to a younger generation of gay men.71
The one thing the experts agreed on was that as unprotected sex increased, HIV infection rates were liable to do so as well.72
But that did not happen. Other STDs did increase: the number of new syphilis diagnoses among men who have sex with men (MSM)73-which had been virtually eradicated from San Francisco in the 1990s-rose substantially, to 502 cases in 2004 from 9 in 1998.74 Rates of gonorrhea also increased. Paradoxically, however, the number of new HIV cases did not rise. In 2004, when syphilis reached its highest level in years, the number of HIV diagnoses fell to their lowest figure since the start of the AIDS epidemic. This made very little sense to researchers; syphilis and HIV are normally strongly correlated statistically, and they also have a causal relationship, since having one disease can make you more vulnerable to acquiring the other one.75
The solution to the paradox, it now appears, is that gay men had become increasingly effective at "serosorting"-that is, they were choosing sex partners with the same HIV status that they had. How they were able to accomplish this is a subject of some debate, but it has been documented by detailed behavioral studies in San Francisco,76 Sydney,77 London, and other cities with large gay populations. It may be that public health campaigns-some of which, wary of "condom fatigue," instead focused on the notion of "negotiated safety"-were having some positive effect. It may be that the Internet, which to some extent has displaced the gay bar as the preferred place to pick up a sex partner, has different norms for disclosure: many men list their HIV status in their profiles, and it may be easier to ask tough questions (and to get honest responses) from the privacy of one's home than in the din of the dance hall.78
Shared publicly