Table 2.

Distribution of subjects according to their lifetime occupational exposure to crystalline silica

ExposureStudy I (1979-1986)Study II (1996-2001)
Population controlsCancer controlsCasesPopulation controlsCases
n (%)n (%)n (%)n (%)n (%)
Unexposed422 (79.2)1,055 (78.2)623 (72.7)721 (80.2)560 (75.9)
Nonsubstantial exposure*82 (15.4)212 (15.7)152 (17.7)140 (15.6)139 (18.8)
Substantial exposure*29 (5.4)82 (6.1)82 (9.6)38 (4.2)39 (5.3)
  • *Distinction between substantial and nonsubstantial is based on estimated concentration, frequency, duration, and latency of exposure, as described in text.