Table 1

Criteria for defining exposure groups for each substance, Montreal, 1979–85

Exposure group^1-150	Confidence	Years since first exposure	Concentration × frequency^1-151	Duration (y)
Excluded	Possible	Any	Any	Any
Excluded	Any	⩽5	Any	Any
Unexposed	—	—	—	None
Non-substantial	Probable or definite	>5	<4	Any
Non-substantial	Probable or definite	>5	⩾4	⩽5
Substantial	Probable or definite	>5	⩾4	>5

↵1-150 For each exposure group, all criteria listed on each row must be fulfilled.
↵1-151 Concentration and frequency are scored as follows: 1=low; 2=medium; 3=high.