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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
".