Table 4 Mean translocation frequency/100 cell equivalents and rate ratios by exposure status and flight years
n (%)UnivariateMultivariate*
Mean (SE)Rate ratios†(Wald 95% CI)Mean (SE)‡Rate ratios(Wald 95% CI)
Model 1
    Exposure status
        Comparison group50 (37.6%)0.32 (0.05)1.000.38 (0.06)1.00
        Pilots83 (62.4%)0.39 (0.04)1.25 (0.92 to 1.70)0.37 (0.04)0.98 (0.65 to 1.48)
Model 2 (pilots only)
    Flight years§
        <13.1721 (25.3%)0.27 (0.05)1.000.23 (0.10)1.00
        13.17–17.4920 (24.1%)0.42 (0.08)1.50 (0.93 to 2.41)0.38 (0.08)1.39 (0.87 to 2.23)
        17.50–23.2421 (25.3%)0.27 (0.06)1.01 (0.62 to 1.65)0.30 (0.07)1.06 (0.57 to 1.97)
        ⩾23.2521 (25.3%)0.61 (0.08)2.23 (1.42 to 3.52)0.66 (0.09)2.59 (1.26 to 5.33)
        p Trend¶0.0030.007
  • *Adjusted for age (41–45, 46–50 or >50 vs ⩽40 years), cumulative red bone marrow x ray dose score (0.5–1.9 or ⩾2.0 vs <0.5) and military flying (yes vs no) as categorical variables; †derived from the exponentiation of the corresponding negative binomial regression coefficient; ‡derived from a linear model using analysis of covariance; SE involved pooling of unequal variance; §categorised by quartile cut points based on the flight year distribution of pilots; ¶derived from negative binomial regression model treating the medians of quartiles of flight years as a continuous variable.

  • SE, standard error.