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
Univariate	1.02 (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
Univariate	1.04 (1.02 to 1.07)	0.003
Multivariate	1.06 (1.01 to 1.11)	0.01
10-year increment
Univariate	1.54 (1.16 to 2.02)	0.003
Multivariate	1.81 (1.16 to 2.82)	0.01
Stratified by age intervals¶
1-year increment
Univariate
37−42	1.02 (0.94 to 1.10)	0.59
43−48	1.00 (0.93 to 1.07)	0.90
49−55	1.07 (1.02 to 1.12)	0.005
Multivariate
37−42	1.06 (0.94 to 1.18)	0.32
43−48	1.05 (0.96 to 1.15)	0.32
49−55	1.08 (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).