Table 5

Mixed model coefficients and standard errors for estimated log fibre concentrations (fibres >5 μm/ml) by plant, exposure zone, calendar period and job group, North Carolina asbestos textile plants

Model fixed effectsPlantZone and departmentUJCβ CoefficientSE
Intercept2.6360.632
Follow-up year (Year-1935)−0.0580.012
Spline 1 (Year-46, If >0)*−0.0160.016
Spline 2 (Year-64, If >0)0.0290.012
Spline 3 (Year-71, If >0)−0.2100.025
Spline 4 (Year-76, If >0)0.0920.028
UJCs nested within zones and plants11-PreparationA1.2810.675
11-PreparationB1.6590.650
11-PreparationD2.1130.735
12-CardingA1.6580.639
12-CardingB1.6130.670
12-CardingD2.1980.767
13-SpinningA0.6030.640
13-SpinningB1.2000.648
14-TwistingA0.7580.646
14-TwistingB1.3440.653
15-WeavingA−0.3290.651
15-WeavingB−0.1230.644
31-PreparationA1.2410.634
31-PreparationB1.6210.634
31-PreparationD1.3710.650
32-CardingA1.5950.632
32-CardingB1.9160.631
32-CardingD1.6100.659
33-SpinningA0.2920.637
33-SpinningB0.9200.631
34-TwistingA0.3070.641
34-TwistingB1.5530.632
35-WeavingA1.6040.640
35-WeavingB1.0330.629
41-PreparationA1.6080.670
41-PreparationB1.6830.639
41-PreparationD2.2310.723
42-CardingA1.6100.635
42-CardingB1.6960.636
42-CardingD2.9080.705
43-SpinningA1.9130.649
43-SpinningB1.9380.640
44-TwistingA2.2790.661
44-TwistingB1.9260.643
45-WeavingA1.2790.643
45-WeavingB1.5730.631
  • Example arithmetic mean PCM concentration calculation for a weaver (UJC B) in plant 1 in 1955. Model residual variance = 1.169.

  • AM = exp[(intercept+(βyear)×(1955–1935)+(βspline_1)×(1955–1946)+βUJC zone plant+0.5×(residual model variance)]

  • AM = exp[2.636+(−0.058×20)+(−0.016×9)+(−0.123)+(0.5×1.169)]

  • AM = 6.01 fibres>5 μm/ml

  • *In linear spline time trends the coefficients for the second term through remaining terms are constrained to apply only when the variable (year-boundary) is a positive value.

  • A, arithmetic mean; PCM, phase contract microscopy; SE, standard error; UJC, uniform job category.