Table 3.

Definition of rating scores used to assess the study strength.

Parameter	Score assigned
	2	1	0
Exposure assessment	Specific biomarkers (e.g., blood chlorpyrifos)	General biomarkers (e.g., DAP metabolites)	Ecological dataa; Hospital records of intoxication or poisoning
Neurodevelopmental assessmentb	Standardized, well-validated tests for diagnostic or neurobiologically based markers of development	Screening tests, interviews, checklists or questionnaires. Older versions of well validated tests. Not widely used tests in neurodevelopmental assessment	Selected sections of full test batteries
Study design	Longitudinal, exposures precede outcome	Case control	Cross-sectional, case study
Sample size	>200	≥50	<50
Confounder control	Good control for important confoundersc and standard variables	Standard variables controlled in analysesd	Not considered

Categories of rating: 0–2 = low rating, 3–7 = intermediate rating, 8–10 = high rating.

^aEcological data: Exposure assumed by the proximity to places where pesticides were applied or in children or adolescents that worked in farms.

^bFor specific characteristics of the neurodevelopmental assessment instruments see Table 2.

^cImportant confounders to control in this class of studies could be: Parental intelligence, quality of the home environment, potential factors on the causal pathway (birth weight, gestational age, abnormal reflexes), other suspected neuro-toxicants (i.e., PCBs, lead, and DDT), other high-level exposures in the population (i.e., β-hexachlorocyclohexane and hexa-chlorobenzene), exposure to environmental tobacco smoke (ETS).

^dStandard variables considered: age, sex, education, income, race/ethnicity.