Table 3 Frequency of different dimensions of exposure to cotton dust and wool dust in two studies in Montreal, Canada, cases and controls combined

Level of exposure

      Non-substantial

4.1

17.2

2.5

7.4

      Substantial

4.0

1.6

3.4

1.0

Exposure concentration^a

      Low

2.6

15.9

1.6

6.9

      Medium

4.2

2.4

3.8

1.4

      High

1.3

0.5

0.5

0.2

Confidence level^a

      Possible

0.1

2.0

0.04

1.1

      Probable

1.3

5.1

1.1

1.9

      Definite

6.7

11.7

4.8

5.5

Frequency ^a

      <5% of work week

0.3

0.4

0.3

0.2

      5-30% of work week

1.6

3.8

1.4

1.7

      >30% of work week

6.2

14.4

4.3

6.5

Duration

      1-5 years

2.2

7.7

1.3

3.5

      6-20 years

3.1

6.9

2.2

3.3

      >20 years

2.8

4.2

2.4

1.6