O’Connor et al. systematic review regarding animal feeding operations and public health: critical flaws may compromise conclusions

Abstract

In this comment, we summarize several scientific concerns with the recently published systematic review from O’Connor and colleagues that examined the relationship between proximity to animal-feeding operations and health of individuals in nearby communities. The authors utilized a bias tool not designed for environmental health research, erroneously excluded important studies, and incorrectly interpreted others. As a result, the conclusions drawn in the review misrepresent the evidence from the published literature, limiting its value to policymakers, researchers, and the public.

Authors’ response to comments from Nachman KE et al.

“…We relayed our experiences with the tool to the authors of ROBINS-I so that our feedback could be incorporated into ongoing development of a tool to assess risk of bias in exposure studies [ 5 ]. We note that the draft version of this new tool for exposure studies is remarkably similar to ROBINS-I, so we do not agree with Nachman KE et al [ 2 ] that a different approach is required in environmental health research. Nachman KE et al [ 2 ] appear to place a higher evidentiary value on observational studies than we are willing to place.…”

“…That our systematic review has generated debate is not surprising, as this is an important and divisive topic [ 1 ]. Nachman KE et al [ 2 ] stated that they would have conducted the review with different eligibility criteria and risk-of-bias assessment. It is to be expected that different review teams will make slightly different judgements about the breadth of their review and the types of studies they consider appropriate to include.…”

“…We invite readers to read the Open Peer Reports of our original submission for more details of the decisions we made, including discussion about how we considered residual confounding in observational studies, the use of prevalent outcomes, chronic and acute disease, multiplicity, the age of data reported in studies, and effect measures obtained from observational studies. Below, we address specific comments made by Nachman KE et al [ 2 ].…”

“…The tool has been carefully developed by a large team and is based on the latest thinking in causal inference. Contrary to the impression portrayed by Nachman KE et al [ 2 ], we modified the tool to ensure applicability to non-interventional exposures. For example, we omitted the domain that asks about adherence to interventions, we modified some elements, and we added details about exposure measurement.…”

“…For example, we omitted the domain that asks about adherence to interventions, we modified some elements, and we added details about exposure measurement. Nachman KE et al [ 2 ] question our inclusion of a question about whether post-intervention variables could influence study participation. To rule out selection bias, however, it is important to determine that post- exposure variables did not influence study participation.…”