Table 1 Selected characteristics for the Vermont granite workers study, 1950–94: comparison of prevalent and incident hires
Prevalent hires* (n = 2603)Incident hires† (n = 2578)
Mean‡ (SD)Mean (SD)
Lung cancer deaths
    Age at death67.2 (8.8)61.7 (9.6)
Time-independent
    Year of hire1932 (13)1961 (7)
    Age at hire24.2 (7.7)28.1 (9.4)
Time-varying§
    Duration of follow-up28.3 (13.8)31.5 (8.0)
    Duration of work30.9 (13.1)10.5 (9.4)
    Time since hire46.0 (11.5)31.5 (8.0)
    Calendar year at risk1977 (10)1984 (9)
    Cumulative silica
        15-year lag, mg-year/m33.7 (4.6)0.3 (0.4)
        Range(0 to 48.2)(0 to 2.0)

  • SD, standard deviation.

  • *Subjects who were already at work prior to the start of follow-up on 1 January 1950 and still at work on that date, includes 157 cases.

  • †Subjects who started working in the granite industry between 1 January 1950 (the start of follow-up) and 31 December 1982; includes 56 cases.

  • ‡All mean differences between prevalent and incident hires were statistically significant (p<0.001).

  • §Time-varying variables evaluated for each subject at the end of follow-up.