By Paul Homewood

We have looked at claims in the past about the number of deaths caused by air pollution.

This article published last year also casts grave doubts about similar claims made in France:

The recent presentation of the French government’s anti-pollution plan was an opportunity for many in the media to remind us of a significant figure: air pollution from fine particles is estimated to cause 48,000 deaths per year in France. Despite its surprising nature (this would mean that about 9% of all deaths were caused by pollution), this figure was treated with few reservations in the press, and even less in political circles (Anne Hidalgo had already used this argument in 2017 for the City of Paris’ anti-pollution plan) It is true that it comes from an irreproachable source, as it is a report by the Agence Santé Publique France (SPF)[i] [Public Health Agency France], which estimated the number of premature deaths attributable in France to PM 2.5 particles (particles with a radius less than or equal to 2.5 mm), using a new mathematical model, based on a map of spatialised air pollution over the entire French territory, at the municipal level. But can this figure of 48,000 deaths be taken as a basis for consideration without reservations? And what exactly does it measure? A careful reading of the SPF report reveals some surprises…

A range of uncertainty between 11 and 48,000 deaths!

The first note of caution (the only one mentioned in the SPF press release, and therefore the only one sometimes taken into account by the more vigilant media) is to state that 48,000 is only the top of a particularly gaping range of uncertainty. In fact, the number of premature deaths calculated by the SPF model varies considerably according to the basic level of pollution considered as “normal”: from 48,000 annual deaths if we take as a reference the least polluted parts of French territory… to 11 deaths if we take as a reference the threshold of fine particles recommended by the WHO ! It is clear, however, that SPF clearly favours a maximising interpretation of 48,000 deaths, and this is the only figure cited by most of the newspapers that reported on this publication. Even if the SPF does not express it very explicitly, it therefore amounts to severely criticising the current standards on air pollution. The INVS [Institut de veille sanitaire, Public Health Surveillance] (now part of SPF) had already questioned these standards in a previous study, which focused on short-term deaths caused by pollution[ii] peaks… forgetting in passing its own work on the effects of the heat wave (the short-term effects of pollution tend to occur only during summer pollution peaks, and not in winter[iii]).

A purely theoretical result, presented as an established truth

On such a serious subject, it therefore seems necessary to examine the arguments and the method employed by SPF in meticulous detail.  From this point of view, the report presents some surprising gaps:

• It contains NO results validating the model used, i.e. no comparison between the mortalities calculated according to their model in each commune, and the actual recorded mortalities. When the authors tell us that their model is an accurate representation of reality, we are therefore obliged to take their word for it.
• This calculation is based on the application of a relative risk (RR), which defines the relationship between mortality and fine particle concentration in the air. In the usual publications on this subject, this RR is statistically calculated by combining a mortality data set with pollution data covering the same geographical area. This is not the method followed by SPF, which in this report has calculated mortalities directly from its spatialised pollution map, with an RR chosen by the authors. This choice of methodology is all the more audacious as the value used is very high compared to existing bibliographical references: RR=1.15 for an increase of 10 μg/m³, i.e. more than double the values used by the previous meta-analyses that the authors cite in their bibliography (0.6 and 0.7). The only justification for this surprising choice is that this value has already been observed in France (by the same SPF authors, there being no better reference than oneself…). Why not, but we would still like to know the RR value that would have been obtained directly from the actual mortality data at the commune level. Once again, an essential element for validation of the SPF model is missing from the report.
• To be scientifically sound, the authors show results from a sensitivity analysis, which theoretically allows the robustness of the model’s predictions to be assessed, based on the uncertainty in its input data. Unfortunately, this analysis only covers relatively secondary parameters, and dodges the essential question, linked to the previous point: what is the effect of uncertainty on Relative Risk, in estimating the number of premature deaths? For example, we would like to know what would have happened to the results if SPF had used a more conventional RR of 0.6 or 0.7.

Read the full article here.

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July 7, 2019 at 07:57AM