100.000 morti in Iraq per la guerra? una patacca!

In Origine Postato da Italosloveno
una ricerca talmente attendibile che il risultato di 100.000 morti e' la media del seguente margine d'errore statistico, quello che i sinistri mi hanno insegnato recentemente a proposito di Repubblica :

8.000 - 194.000

una ricerca patacca, insomma.

http://www.weeklystandard.com/Conten...4/858gwbza.asp

..ma e' ovvio che e' una patacca,..se poi c'e' scritto su Repubblica, come fa a non essere una patacca..???....

[locke (POL)]

http://www.economist.com/science/dis...ory_id=3352814


The Iraqi war

Counting the casualties

Nov 4th 2004
From The Economist print edition

A statistically based study claims that many more Iraqis have died in the conflict than previous estimates indicated

THE American armed forces have long stated that they do not keep track of how many people have been killed in the current conflict in Iraq and, furthermore, that determining such a number is impossible. Not everybody agrees. Adding up the number of civilians reported killed in confirmed press accounts yields a figure of around 15,000. But even that is likely to be an underestimate, for not every death gets reported. The question is, how much of an underestimate?

A study published on October 29th in the Lancet, a British medical journal, suggests the death toll is quite a lot higher than the newspaper reports suggest. The centre of its estimated range of death tolls—the most probable number according to the data collected and the statistics used—is almost 100,000. And even though the limits of that range are very wide, from 8,000 to 194,000, the study concludes with 90% certainty that more than 40,000 Iraqis have died.

Numbers, numbers, numbers



This is an extraordinary claim, and so requires extraordinary evidence. Is the methodology used by Les Roberts of the Johns Hopkins University School of Public Health, in Baltimore, and his colleagues, sound enough for reliable conclusions to be drawn from it?

The bedrock on which the study is founded is the same as that on which opinion polls are built: random sampling. Selecting even a small number of individuals randomly from a large population allows you to say things about the whole population. Think of a jar containing a million marbles, half of them red and half blue. Choose even 100 of these marbles at random and it is very, very unlikely that all of them would be red. In fact, the results would be very close to 50 of each colour.

The best sort of random sampling is one that picks individuals out directly. This is not possible in Iraq because no reliable census data exist. For this reason, Dr Roberts used a technique called clustering, which has been employed extensively in other situations where census data are lacking, such as studying infectious disease in poor countries.

Clustering works by picking out a number of neighbourhoods at random—33 in this case—and then surveying all the individuals in that neighbourhood. The neighbourhoods were picked by choosing towns in Iraq at random (the chance that a town would be picked was proportional to its population) and then, in a given town, using GPS—the global positioning system—to select a neighbourhood at random within the town. Starting from the GPS-selected grid reference, the researchers then visited the nearest 30 households.

In each household, the interviewers (all Iraqis fluent in English as well as Arabic) asked about births and deaths that had occurred since January 1st 2002 among people who had lived in the house for more than two months. They also recorded the sexes and ages of people now living in the house. If a death was reported, they recorded the date, cause and circumstances. Their deductions about the number of deaths caused by the war were then made by comparing the aggregate death rates before and after March 18th 2003.

They interviewed a total of 7,868 people in 988 households. But the relevant sample size for many purposes—for instance, measuring the uncertainty of the analysis—is 33, the number of clusters. That is because the data from individuals within a given cluster are highly correlated. Statistically, 33 is a relatively small sample (though it is the best that could be obtained by a small number of investigators in a country at war). That is the reason for the large range around the central value of 98,000, and is one reason why that figure might be wrong. (Though if this is the case, the true value is as likely to be larger than 98,000 as it is to be smaller.) It does not, however, mean, as some commentators have argued in response to this study, that figures of 8,000 or 194,000 are as likely as one of 98,000. Quite the contrary. The farther one goes from 98,000, the less likely the figure is.

The second reason the figure might be wrong is if there are mistakes in the analysis, and the whole exercise is thus unreliable. Nan Laird, a professor of biostatistics at the Harvard School of Public Health, who was not involved with the study, says that she believes both the analysis and the data-gathering techniques used by Dr Roberts to be sound. She points out the possibility of “recall bias”—people may have reported more deaths more recently because they did not recall earlier ones. However, because most people do not forget about the death of a family member, she thinks that this effect, if present, would be small. Arthur Dempster, also a professor of statistics at Harvard, though in a different department from Dr Laird, agrees that the methodology in both design and analysis is at the standard professional level. However, he raises the concern that because violence can be very localised, a sample of 33 clusters really might be too small to be representative.

This concern is highlighted by the case of one cluster which, as the luck of the draw had it, ended up being in the war-torn city of Fallujah. This cluster had many more deaths, and many more violent deaths, than any of the others. For this reason, the researchers omitted it from their analysis—the estimate of 98,000 was made without including the Fallujah data. If it had been included, that estimate would have been significantly higher.

The Fallujah data-point highlights how the variable distribution of deaths in a war can make it difficult to make estimates. But Scott Zeger, the head of the department of biostatistics at Johns Hopkins, who performed the statistical analysis in the study, points out that clustered sampling is the rule rather than the exception in public-health studies, and that the patterns of deaths caused by epidemics are also very variable by location.

The study can be both lauded and criticised for the fact that it takes into account a general rise in deaths, and not just that directly caused by violence. Of the increase in deaths (omitting Fallujah) reported by the study, roughly 60% is due directly to violence, while the rest is due to a slight increase in accidents, disease and infant mortality. However, these numbers should be taken with a grain of salt because the more detailed the data—on causes of death, for instance, rather than death as a whole—the less statistical significance can be ascribed to them.

So the discrepancy between the Lancet estimate and the aggregated press reports is not as large as it seems at first. The Lancet figure implies that 60,000 people have been killed by violence, including insurgents, while the aggregated press reports give a figure of 15,000, counting only civilians. Nonetheless, Dr Roberts points out that press reports are a “passive-surveillance system”. Reporters do not actively go out to many random areas and see if anyone has been killed in a violent attack, but wait for reports to come in. And, Dr Roberts says, passive-surveillance systems tend to undercount mortality. For instance, when he was head of health policy for the International Rescue Committee in the Congo, in 2001, he found that only 7% of meningitis deaths in an outbreak were recorded by the IRC's passive system.

The study is not perfect. But then it does not claim to be. The way forward is to duplicate the Lancet study independently, and at a larger scale. Josef Stalin once claimed that a single death is a tragedy, but a million deaths a mere statistic. Such cynicism should not be allowed to prevail, especially in a conflict in which many more lives are at stake. Iraq seems to be a case where more statistics are sorely needed.

La notizia (diciamo così) di The Lancet, secondo cui in Iraq sarebbero morti 100 mila civili, è basata su un sondaggio, sì su un sondaggio. E' ridicolo, ma è così. L'Economist lo prende sul serio però, per smontarlo. Severgnini, ex corrispondente dell'Economist, spaccia per vera la notizia e accusa sul Corriere di oggi gli americani ignoranti di non conoscerla: "Pochi sanno che la guerra in Iraq è già costata la vita a centomila civili". Ancora: perché il Corriere è diventato così?
11 novembre

Cordiali Saluti

[ScimmioneNudo]

In Origine Postato da locke
http://www.economist.com/science/dis...ory_id=3352814


The Iraqi war

Counting the casualties

Nov 4th 2004
From The Economist print edition

A statistically based study claims that many more Iraqis have died in the conflict than previous estimates indicated

THE American armed forces have long stated that they do not keep track of how many people have been killed in the current conflict in Iraq and, furthermore, that determining such a number is impossible. Not everybody agrees. Adding up the number of civilians reported killed in confirmed press accounts yields a figure of around 15,000. But even that is likely to be an underestimate, for not every death gets reported. The question is, how much of an underestimate?

A study published on October 29th in the Lancet, a British medical journal, suggests the death toll is quite a lot higher than the newspaper reports suggest. The centre of its estimated range of death tolls—the most probable number according to the data collected and the statistics used—is almost 100,000. And even though the limits of that range are very wide, from 8,000 to 194,000, the study concludes with 90% certainty that more than 40,000 Iraqis have died.

Numbers, numbers, numbers



This is an extraordinary claim, and so requires extraordinary evidence. Is the methodology used by Les Roberts of the Johns Hopkins University School of Public Health, in Baltimore, and his colleagues, sound enough for reliable conclusions to be drawn from it?

The bedrock on which the study is founded is the same as that on which opinion polls are built: random sampling. Selecting even a small number of individuals randomly from a large population allows you to say things about the whole population. Think of a jar containing a million marbles, half of them red and half blue. Choose even 100 of these marbles at random and it is very, very unlikely that all of them would be red. In fact, the results would be very close to 50 of each colour.

The best sort of random sampling is one that picks individuals out directly. This is not possible in Iraq because no reliable census data exist. For this reason, Dr Roberts used a technique called clustering, which has been employed extensively in other situations where census data are lacking, such as studying infectious disease in poor countries.

Clustering works by picking out a number of neighbourhoods at random—33 in this case—and then surveying all the individuals in that neighbourhood. The neighbourhoods were picked by choosing towns in Iraq at random (the chance that a town would be picked was proportional to its population) and then, in a given town, using GPS—the global positioning system—to select a neighbourhood at random within the town. Starting from the GPS-selected grid reference, the researchers then visited the nearest 30 households.

In each household, the interviewers (all Iraqis fluent in English as well as Arabic) asked about births and deaths that had occurred since January 1st 2002 among people who had lived in the house for more than two months. They also recorded the sexes and ages of people now living in the house. If a death was reported, they recorded the date, cause and circumstances. Their deductions about the number of deaths caused by the war were then made by comparing the aggregate death rates before and after March 18th 2003.

They interviewed a total of 7,868 people in 988 households. But the relevant sample size for many purposes—for instance, measuring the uncertainty of the analysis—is 33, the number of clusters. That is because the data from individuals within a given cluster are highly correlated. Statistically, 33 is a relatively small sample (though it is the best that could be obtained by a small number of investigators in a country at war). That is the reason for the large range around the central value of 98,000, and is one reason why that figure might be wrong. (Though if this is the case, the true value is as likely to be larger than 98,000 as it is to be smaller.) It does not, however, mean, as some commentators have argued in response to this study, that figures of 8,000 or 194,000 are as likely as one of 98,000. Quite the contrary. The farther one goes from 98,000, the less likely the figure is.

The second reason the figure might be wrong is if there are mistakes in the analysis, and the whole exercise is thus unreliable. Nan Laird, a professor of biostatistics at the Harvard School of Public Health, who was not involved with the study, says that she believes both the analysis and the data-gathering techniques used by Dr Roberts to be sound. She points out the possibility of “recall bias”—people may have reported more deaths more recently because they did not recall earlier ones. However, because most people do not forget about the death of a family member, she thinks that this effect, if present, would be small. Arthur Dempster, also a professor of statistics at Harvard, though in a different department from Dr Laird, agrees that the methodology in both design and analysis is at the standard professional level. However, he raises the concern that because violence can be very localised, a sample of 33 clusters really might be too small to be representative.

This concern is highlighted by the case of one cluster which, as the luck of the draw had it, ended up being in the war-torn city of Fallujah. This cluster had many more deaths, and many more violent deaths, than any of the others. For this reason, the researchers omitted it from their analysis—the estimate of 98,000 was made without including the Fallujah data. If it had been included, that estimate would have been significantly higher.

The Fallujah data-point highlights how the variable distribution of deaths in a war can make it difficult to make estimates. But Scott Zeger, the head of the department of biostatistics at Johns Hopkins, who performed the statistical analysis in the study, points out that clustered sampling is the rule rather than the exception in public-health studies, and that the patterns of deaths caused by epidemics are also very variable by location.

The study can be both lauded and criticised for the fact that it takes into account a general rise in deaths, and not just that directly caused by violence. Of the increase in deaths (omitting Fallujah) reported by the study, roughly 60% is due directly to violence, while the rest is due to a slight increase in accidents, disease and infant mortality. However, these numbers should be taken with a grain of salt because the more detailed the data—on causes of death, for instance, rather than death as a whole—the less statistical significance can be ascribed to them.

So the discrepancy between the Lancet estimate and the aggregated press reports is not as large as it seems at first. The Lancet figure implies that 60,000 people have been killed by violence, including insurgents, while the aggregated press reports give a figure of 15,000, counting only civilians. Nonetheless, Dr Roberts points out that press reports are a “passive-surveillance system”. Reporters do not actively go out to many random areas and see if anyone has been killed in a violent attack, but wait for reports to come in. And, Dr Roberts says, passive-surveillance systems tend to undercount mortality. For instance, when he was head of health policy for the International Rescue Committee in the Congo, in 2001, he found that only 7% of meningitis deaths in an outbreak were recorded by the IRC's passive system.

The study is not perfect. But then it does not claim to be. The way forward is to duplicate the Lancet study independently, and at a larger scale. Josef Stalin once claimed that a single death is a tragedy, but a million deaths a mere statistic. Such cynicism should not be allowed to prevail, especially in a conflict in which many more lives are at stake. Iraq seems to be a case where more statistics are sorely needed.

La notizia (diciamo così) di The Lancet, secondo cui in Iraq sarebbero morti 100 mila civili, è basata su un sondaggio, sì su un sondaggio. E' ridicolo, ma è così. L'Economist lo prende sul serio però, per smontarlo. Severgnini, ex corrispondente dell'Economist, spaccia per vera la notizia e accusa sul Corriere di oggi gli americani ignoranti di non conoscerla: "Pochi sanno che la guerra in Iraq è già costata la vita a centomila civili". Ancora: perché il Corriere è diventato così?
11 novembre

Cordiali Saluti

L'america ai pellerossa? No agli statunitenti.
La palestina ai palestinesi? No agli israeliani.

E l'Iraq?

Domani tutti a occupare la casa di locke.

Ai coerenti.

[locke (POL)]

In Origine Postato da ScimmioneNudo
L'america ai pellerossa? No agli statunitenti.
La palestina ai palestinesi? No agli israeliani.

E l'Iraq?

Domani tutti a occupare la casa di locke.

Ai coerenti.

Sono in affitto, se vuoi venire e condividere le poche spese...ti aspetto domani mattina ti svegli tu alle 5 am ad accudiere il filgioletto?

Cordiali Saluti

Ps La slesia a tedeschi? No ai Polacchi, non è che i tedeschi hanno perso una guerra?

[ago]

In realta' si nota solo che la varianza della stima e' necessariamente elevata. Ma la metodologia e' quella corretta....

Anzi si sottolinea che l'unico modo di far meglio e' di fare ESATTAMENTE come Lancet ma con un maggior numero di campioni... Come dicevo sopra...

The way forward is to duplicate the Lancet study independently, and at a larger scale

Evidentemente anche l'economist e' d'accordo che questa e' la metodologia migliore possibile...

Tra l'altro, il fatto che la varianza sia elevata e' un problema relativo, visto che il livello di incertezza e' quasi CERTO.... Ed il livello di incertezza gia' incorpora le problematiche relative alle dimensioni del campione. Uno dei vantaggi della statistica e' proprio quello di affermare con relativa certezza il livello dell'incertezza e ad esempio sappiamo che il valore di gran lunga piu' probabile e' 98000 e c'e' appena un 10% di probabilita' che i morti siano stati in realta' 40.000.

Leggere bene:

It does not, however, mean, as some commentators [e pollisti] have argued in response to this study, that figures of 8,000 or 194,000 are as likely as one of 98,000. Quite the contrary. The farther one goes from 98,000, the less likely the figure is.

Esattamente quello che vi dicevo io...

Niente di nuovo sotto il sole, 98000 e' e resta la stima MIGLIORE OGGI DISPONIBILE.

E la stima "diretta" basata sui press reports sottostima il dato reale poiche':

Roberts points out that press reports are a “passive-surveillance system”. Reporters do not actively go out to many random areas and see if anyone has been killed in a violent attack, but wait for reports to come in. And, Dr Roberts says, passive-surveillance systems tend to undercount mortality.

[ago]

Bananas almeno cercate di leggere quello che postate...

Nan Laird, a professor of biostatistics at the Harvard School of Public Health, who was not involved with the study, says that she believes both the analysis and the data-gathering techniques used by Dr Roberts to be sound

Arthur Dempster, also a professor of statistics at Harvard, though in a different department from Dr Laird, agrees that the methodology in both design and analysis is at the standard professional level

[IlikeUSA]

In Origine Postato da ScimmioneNudo
L'america ai pellerossa? No agli statunitenti.
La palestina ai palestinesi? No agli israeliani.

E l'Iraq?

Ai coerenti.

Ehi babbuinonudo, a chi la diamo l'Istria? La Prussia? I Sudeti?
Agli autoctoni cacciati o ai vostri amici comunisti perchè hanno vinto la guerra?
Ai pacifinti.

[locke (POL)]

....So the discrepancy between the Lancet estimate and the aggregated press reports is not as large as it seems at first. The Lancet figure implies that 60,000 people have been killed by violence, including insurgents, while the aggregated press reports give a figure of 15,000, counting only civilians. Nonetheless, Dr Roberts points out that press reports are a “passive-surveillance system”. Reporters do not actively go out to many random areas and see if anyone has been killed in a violent attack, but wait for reports to come in. And, Dr Roberts says, passive-surveillance systems tend to undercount mortality. For instance, when he was head of health policy for the International Rescue Committee in the Congo, in 2001, he found that only 7% of meningitis deaths in an outbreak were recorded by the IRC's passive system.

......


Cordiali Saluti

[locke (POL)]

In Origine Postato da Ago
Bananas almeno cercate di leggere quello che postate...

Secondo te l'articolo critica lo studio del The Lancet?

Cordiali Saluti

[ago]

In Origine Postato da locke
Secondo te l'articolo critica lo studio del The Lancet?

Cordiali Saluti

Assolutamente NO

Dice che la metodologia e' corretta, infatti invita a DUPLICARE lo studio...

"The way forward is to duplicate the Lancet study independently, and at a larger scale."

Si nota che sarebbe meglio avere maggiori campioni, per ridurre la varianza, ovvero l'incertezza della stima, cosa che facevo gia' notare sopra. Ma avere piu' campioni significa avere persone che sono in Iraq a rischiare la vita per raccogliere informazioni ed molto e' piu' facile a dirsi che a farsi.... In ogni modo l'ampiezza del campione e' gia' riflessa nei dati tramite la varianza della stima e quindi nell'intervallo di confidenza...

Ad oggi questa resta la ricerca MIGLIORE come metodologia e come estensione del campione. Se e quando ci sara' una ricerca piu' ampia se ne riparlera', per ora il dato di 98.000 e' il migliore oggi disponibile.

Il numero di 60000 e' un sottoninsime di 98000, che include solo le morti VIOLENTE (ad essere precisi e' il valore atteso delle morti violente). Invece 98000 include TUTTI I DECESSI IN PIU' rispetto alla situazione pre-guerra. Ovvero non solo le morti violente ma conta anche coloro che sono stati colpiti "indirettamente" dalla guerra come il signore che schiatta in ospedale perche' viene meno la corrente a causa di una bomba ad un chilometro... Morti che non ci sarebbero se non ci fosse il conflitto e morti che non sono mai contate nelle altre statistiche "dirette" ma che ovviamente vanno incluse.