Analysis of Evidence: Air Pollution as Cause of Mental Disease

This report critically examines the evidence linking air pollution to mental diseases, particularly focusing on the work of Ioannidis (2019). The analysis explores the challenges in establishing a causal relationship, including data limitations in the US and Denmark studies, and the complexities of assessing individual exposure and mental health diagnoses. The report highlights the moderate strength of the association, the inconsistency between the datasets, and the uncertain temporality of the relationship. It also discusses the biological mechanisms, the lack of experimental evidence, and the need for transparency and reproducibility in research. Despite these limitations, the analysis suggests a positive correlation, especially with bipolar disorder. The conclusion emphasizes the need for further research and the potential implications for policy and treatment.

Air pollution as cause of mental disease:
Appraisal of the evidence

Mental illnesses are predominantly caused by monogenetic factors such as air pollution. The
given report investigates the supposed cause and effect relationship between air pollution and
mental disorders. It explores the shortcomings of such a study and also the possible advantages it
offers.
There are several issues that were faced while determining the nature of the relationship between
air pollution exposure and mental disorders. The large US database posed greater challenges than
the Denmark database. The US population sample was highly selective and information about
metal illness was gathered from the largely unreliable medical claim reports. There was no
assessment of individual exposures to air pollution and no comparison of the medical claim
reports with the results of a thorough clinical diagnosis. On the other, the entire Danish
population was sampled and the assessment was carried out at an individual level (Ioannidis
2019).
A detailed analysis of the Bradford Hill Criteria for causal relationships was carried out.
 The relationship was found to have moderate strength. This observation is quite
acceptable as true causal relationships tend to have modest strengths.
 There was hardly any consistency between the Danish and the US samples. However,
both samples suggested a positive correlation between bipolar disorder and air pollution
exposure.
 The association between the exposure and psychological illness is highly complex and
non specific.
 Temporality is uncertain especially in the American data where it is quite possible that
the onset of the mental disorder took place before the exposure.
 A plausible biological mechanism that explains the cause and effect relation is hard to
determine because of the possibility of selection bias.
 The results are not based on experiment because it is unethical to deliberately expose
participants to air pollution for experimental purposes.
 Analogies did not prove to be helpful as the association of air pollution with respiratory
diseases and increased mortality does not establish any kind of cause and effect
relationship between air pollution and mental disorders (Ioannidis 2019).
It is possible for different analysts to interpret the same set of data and arrive at different results.
In such situations, transparency of data is essential. If different analysts with contradictory
perspectives arrive at the same conclusion, the investigation gains trustworthiness. The data
collected by Khan and colleagues was made available for cross-analysis by other analysts who
arrived at similar conclusions.
Khan and colleagues also responded positively to the peer reviewers who wanted them to prove
the reproducibility of their results. They used different analytical approaches and showed that all
of them yielded similar results.

The introduction of alternative methods of analysis such as the Poisson regression, Cox Models
and the harmonization of variables increased the robustness of the investigation, particularly
when the results of theses analyses were found to be consistent. However, a major drawback of
the investigation was the limited number of psychiatric diagnoses that were reported (Ioannidis
2019).
In a nutshell, Khan and colleagues have provided a thorough analysis of the correlation between
air pollution and mental disorders, particularly in the case of bipolar disorder. This analysis has
opened up new avenues of policy making and new treatment methods for the management of
mental illnesses.

Reference
Ioannidis, John P. A. "Air Pollution As Cause Of Mental Disease: Appraisal Of The
Evidence". PLOS Biology, vol 17, no. 8, 2019, p. e3000370. Public Library Of Science (Plos),
doi:10.1371/journal.pbio.3000370. Accessed 20 Sept 2019.