Table 3 Association between translocation frequency/100 cell equivalents and flight years*
Rate ratios†(Wald 95% CI)p Value‡
Model 1 (pilots and comparison subjects)
    Flight years
        1-year increment
            Univariate1.02 (1.00 to 1.03)0.01
            Multivariate§1.01 (0.99 to 1.03)0.34
Model 2 (pilots only)
    Flight years
        Overall
            1-year increment
                Univariate1.04 (1.02 to 1.07)0.003
                Multivariate1.06 (1.01 to 1.11)0.01
            10-year increment
                Univariate1.54 (1.16 to 2.02)0.003
                Multivariate1.81 (1.16 to 2.82)0.01
        Stratified by age intervals¶
            1-year increment
                Univariate
                    37–421.02 (0.94 to 1.10)0.59
                    43–481.00 (0.93 to 1.07)0.90
                    49–551.07 (1.02 to 1.12)0.005
                Multivariate
                    37–421.06 (0.94 to 1.18)0.32
                    43–481.05 (0.96 to 1.15)0.32
                    49–551.08 (1.03 to 1.13)0.002
  • *Modelled as a continuous variable (coded as 0 for comparison subjects); †derived from the exponentiation of the corresponding negative binomial regression coefficient; ‡for the likelihood ratio χ2 statistic; §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; ¶5-year age intervals: 37–42 (n = 20); 43–48 (n = 28); 49–55 (n = 35).