Table I. Criteria Used for Evaluating Strength of Evidence for a Positive Association Between Styrene Exposure and NMRD-Related Morbidity or Mortality.

	Strong (+++)	Intermediate (++)	Suggestive (+)
Cross-sectional studies	(1) Inclusion of styrene-exposed and comparison groups,a AND	(1) Inclusion of styrene-exposed and comparison groups,a AND	(1) Inclusion of styrene-exposed and comparison groupsa and non-statistically significantb higher prevalence for ≥1 respiratory symptom or ≥1 NMRD, or airflow limitation on spirometry, OR
	(2) exposure group had statistically significantb higher prevalence for ≥1 respiratory symptom or NMRD, AND	(2) exposure group had statistically significantb higher prevalence for ≥1 respiratory symptom or ≥1 NMRD, or airflow limitation on spirometry	(2) no comparison groupa and the presence of exposed workers with respiratory symptoms or ≥1 NMRD, or airflow limitation on spirometry
	(3) exposure group had statistically significant higher prevalenceb for airflow limitation on spirometry
Mortality studies	(1) Analysis of workers by level of styrene exposure, AND	All workers or a subset of workers had statistically significantb higher SMR for ≥1 NMRD	All workers or a subset of workers had non-statistically significantb higher SMR for ≥1 NMRD
	(2) workers with high exposure had statistically significantb higher SMR for ≥1 NMRD

NMRD, non-malignant respiratory disease; SMR, standardized mortality ratio.

^aComparison groups determined by environmental exposure data at factories and include groups with either no or comparatively low styrene exposure.

^bP < 0.05.