Table 1.

PECO statement.

PECO element	Evidence
Population	Human populations or rodent models of autism spectrum disorder.
Exposure	Exposure occurring during prenatal or early life period. Exposure should begin prior to 2 months of age for humans and postnatal day 14 for rats and mice. Exposure can be either gestational (i.e., via maternal exposure) or directly to the offspring. Only environmental chemical exposures are included (e.g., air pollution, pesticides, flame retardants, heavy metals, etc.).
Comparators	Comparison group with lower exposure or no exposure.
Outcome	Autism spectrum disorder or indicators of autism spectrum disorder. Rodent studies need to report at least one reciprocal social communicative behavior or one repetitive and stereotyped behavior.

Note: PECO, populations, exposures, comparators, outcome.