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29231: L Beaulieu (comment) Errors in the Lancet study (fwd)




From: Laurent Beaulieu <laubeaulieu@wanadoo.fr>

The study published by The Lancet shows that there have been many human rights violations, especially sexual assaults. And so it is useful. But it contains some blatant errors. Imagine that you make a survey about the activities of the Haitians. 1000 people have been randomly selected among 8 millions, and Rene Preval is one of them. How will you extraploate to the entire population ? Will you calculate that there are 1 x 8000 = 8000 presidents in Haiti ? No, because you have got another information : there is only one president in Haiti.
The Lancet study contains such kind of gross errors.
Look at the table 3 "Proportion of individuals in zone that were victimized during the period assessed extrapolated to entire population for the zone". According to this table, 0 % of the entire population has been murdered in Martissant/Grand Ravine and in Lavil/Belair! Having found no murder in their sample in these zones, the authors of the study have extrapolated "0%" for the entire population of the zones. It is stupid, because everybody knows that many murders have been documented in these areas. Instead of "0%", they should have written : "We do not know". Look at the table 2 : "Percentages of specified violations committed by specified group, extrapolated to the greater Port-au-Prince area". According to this table, in the greater Port-au-Princie, during 22 months, nobody has been murdered by "partisans of anti Lavalas groups", "Lavalas members or partisans" and "foreign soldiers". Nobody has been murdered by theses groups in the sample ....so Kolbe and Hutson conclude : "none" in Port-au-Prince. They should have written : "We do not know".

The first error of Kolbe and Hutson has been the size of their sample (only 1260 households). It might be the good size to study the age of the population, but not to study human rights violations, especially murders or kidnappings, i.e. "rare" events. The second error has been extrapolating (making projections) when it is impossible. The third error is writing dubious comments. They extrapolate the data of the survey, even when it is a nonsense. In their sample, they have got 23 murders, 5 (or 4 ?) of them being commited by police. What can you extrapolate from 5 ? Nothing, of course. They have found 5 in their sample ; with another sample, they would have found zero, or 10 or anything else. But they absolutely want to make calculations. In every scientifical book about surveys, you can read that you cannot make classical extrapolations when the figures are too small. Meanwihile Kolbe and Hutson calculate very seriously (table 2) that between 2,7% and 40,7% of the murders have been committed by "HNP and other government security forces" (more exactly : the probability for the number of murders committed by this group to belong to the interval [2,7%, 40,7%] is 95% ; and they assume a Poisson distribution with the highest probability around 21,7%). Even if we accept this hazardous extrapolation, it is clear that the "confidence interval" is so wide (from 2,7% to 40,7% !) that the information provided is very small. But Kolbe and Hutson write bluntly that "officers in HNP and members of other government security forces were identified by respondents as committing a SUBSTANCIAL proportion of sexual assaults and murders". For the murders, this assertion is only based on 5 or 4 murders documented in the survey ! Several reports have shown that police officers have killed a lot of people, but not this survey.

There are other gaps between the tables and the comments. They write : "our estimates suggest that about 8000 individuals were murdered, with almost half of the perpetrators identified as political actors". "About 8000 murders" ? According to table 1, the probability for the number of murders to belong to the interval [5000, 12000] is 95%. And, for various reasons, this result suggests that the probability for the number of murders to belong to the interval [6500, 9500] is 67%. Only 67%. "Half of the perpetrators identified as political actors" ? Read table 1 and you will see that this is a very hazardous assertion.

Many people have been surprised that no murder, no sexual assault and no "kidnapping or extra-judicial detention" have been attributed by respondents to "Lavalas members or partisans". I do not think that the data were invented. There are probably several explanations. One of them is that during "Bagdad Operation", media called the armed bands "bandits" . Another explanatition is that for the victims, murderers, rapers and kidnappers are "criminals", not political activists. It is an answer to gang leader William Baptiste, known as Ti Blan, who recently said : "We are not criminals, we are political militants ".