Methodological issues in descriptive environmental epidemiology. The example of study Sentieri

Our plain-English summary of Methodological issues in descriptive environmental epidemiology. The example of study Sentieri, by C. Ciocan, N. Franco, E. Pira, et al (La Medicina del Lavoro, 2021).

The study

• Authors: C. Ciocan, N. Franco, E. Pira, I. Mansour, A. Godono, P. Boffetta
• Journal: La Medicina del Lavoro
• Published: 2021;112(1):15-33
• Type of article: Meta-analysis, Systematic review
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Descriptive epidemiology identifies associations between environmental exposures and health effects that require results from methodologically stronger studies before causation can be considered.

Objective: To critically review the methodology and results of Sentieri, a descripitive study on residence in areas with one or more industrial source of pollution.

Methods: We systematically reviewed the literature quoted by Sentieri for the selection of health effects of nine types of pollution sources of a-priori interest. We also reviewed and meta-analyzed the results of the first report of Sentieri, that analyzed mortality in 44 polluted sites (PS), and 17 causes of deaths during 1995-2002.

Results: Among 159 study results quoted by Sentieri, 23.9 % were supportive of an association between residence near a pollution source and a health effect, 30.2 % were partially supportive, 10.7 % were not supportive, and 35.2 % were not relevant. Among 653 standardized mortality ratios for associations between PS-specific pollution sources and causes of death, 14.4% were significantly above 1.02, and 9.0% were significantly below 0.98. Among 48 meta-analysis, seven were significantly above 1.0, including five on exposure to asbestos.

Conclusions: Sentieri exemplifies the limitations of descriptive environmental epidemiology studies, in which most hypotheses have limited prior support, most results do not show associations, data on potential confounders and other sources of bias are not available. Such studies tend to replicate well-known associations and occasionally can identify critical situations requiring more investigation, but cannot be used to infer causality either in general or in specific circumstances.

In plain English

This article critically reviewed Sentieri, an Italian descriptive study of deaths among residents of 44 polluted sites, and meta-analyzed its published results for 1995-2002. The authors re-checked the 159 study results Sentieri cited to support its choice of health effects for nine types of pollution source. Of these, 23.9% supported an association, 30.2% partly supported one, 10.7% did not, and 35.2% were not relevant. Of 653 sex-specific standardized mortality ratios, 14.4% were significantly raised and 9.0% significantly lowered. Seven of 48 meta-analyses were statistically significant. These included pleural cancer in men (RR 3.28, 95% CI 1.84 to 5.82) and women (RR 2.67, 95% CI 1.13 to 6.30). The results table lists these under sites with an asbestos industry, but the text attributes them to mines. Pleural cancer near harbors was also significant. The authors wrote that the only clearly identified health effect was raised pleural cancer mortality in sites with asbestos sources. They concluded that such studies cannot be used to infer causality. They noted they did not judge the quality of the cited studies.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Critical review of the methods and first mortality report of a descriptive ecologic study (Sentieri), with random-effects meta-analyses of its published standardized mortality ratios
• Who was studied: Residents of 44 Italian polluted sites in 17 regions (298 municipalities), as reported in Sentieri's first report on mortality during 1995-2002 (653 sex-specific SMRs), plus the 159 study results Sentieri cited to support its choice of health effects
• Exposure: Residence near nine types of pollution source: chemical plants, petrochemical plants and oil refineries, iron and steel plants, power plants, mining, harbors, plants using asbestos and other mineral fibres, waste landfills and incinerators
• Main results:
  • Of the 159 results Sentieri cited, 38 (23.9%) supported Sentieri's interpretation, 48 (30.2%) partly supported it, 17 (10.7%) did not support it, and 56 (35.2%) were not relevant
  • Sentieri had judged the evidence sufficient for a causal relationship for only two combinations: mining and pleural cancer, and asbestos and pleural cancer
  • In Sentieri's review of residence near asbestos or other mineral fibre plants, two studies on pleural cancer supported an association
  • Of the 653 SMRs, 94 (14.4%) were significantly higher than 1.02 and 59 (9.0%) were significantly lower than 0.98
  • A test of whether raised and lowered SMRs were evenly distributed gave p = 0.04. With pleural cancer results excluded, it gave p = 0.12
  • In 7 of 48 meta-analyses (15%) the summary RR was statistically significant
  • Pleural cancer: men RR 3.28 (95% CI 1.84 to 5.82, 9 sites); women RR 2.67 (95% CI 1.13 to 6.30, 8 sites). Table 9 lists these under asbestos industry; the text attributes them to mines
  • Lung cancer in men, listed in Table 9 under asbestos industry: RR 1.10 (95% CI 1.01 to 1.19). Women: RR 1.03 (95% CI 0.91 to 1.17), not significant
  • Pleural cancer near harbors: men RR 1.67, women RR 1.32, both statistically significant
  • The authors stated that the only health effect clearly identified in Sentieri was raised pleural cancer mortality in sites with sources of asbestos exposure
  • Most meta-analyses showed high heterogeneity between sites: 30 of 48 (63%) had a heterogeneity test p-value below 0.05
• The authors' conclusion: The authors concluded that Sentieri, like other descriptive environmental epidemiology studies, tends to replicate well-known associations. In their view it cannot be used to infer causality, either in general or in specific circumstances.
• Limitations the authors state:
  • The authors did not evaluate the quality and validity of the studies Sentieri cited, only whether their results supported Sentieri's interpretation
  • The authors did not systematically check whether Sentieri's literature reviews missed relevant studies
  • The authors did not evaluate the overall evidence for each association, including studies published after 2011

Topics

Medical terms in this study, explained in our Lexicon: Epidemiology, Environmental Exposure, Causation, standardized mortality ratio (SMR), Meta-Analysis.

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