Table 3
(a) Mortality associated with age at diagnosis in pediatric patients with leukemia, 1973–2006, in an adjusted multivariable Cox proportional hazard model stratified by the year of diagnosis

CovariatesAdjusted hazard ratio (AHR)99% CI of HR 𝑃

Age at diagnosis (yrs)
 <1.01.0refref
 1.0–4.00.240.21–0.28<0.0001
 5.0-9.00.310.26–0.36<0.0001
 10.0–14.00.540.46–0.62<0.0001
 15.0–19.00.820.70–0.950.001
Sex
 Boys1.0refref
 Girls0.870.81–0.94<0.0001
Race
 White1.0refref
 Black1.471.29–1.65<0.0001
No. of primaries
 1.01.0refref
 ≥ 2.01.301.03–1.630.004
Radiation
 Yes1.0refref
 No1.221.11–1.34<0.0001

Notes and Abbreviations. The significance level was 0.01. CI: Confidence interval.
(b) Mortality associated with age at diagnosis in pediatric patients with Leukemia, 1973–2006, in an adjusted multivariable Cox proportional hazard model stratified by the year of diagnosis in a subset of data with cell type only information

CovariatesAHR99% CI of HR 𝑃

Age at diagnosis (yrs)
 <1.01.0refref
 1.0–4.00.140.10–0.20<0.0001
 5.0–9.00.210.15–0.30<0.0001
 10.0–14.00.380.27–0.54<0.0001
 15.0–19.00.650.46–0.910.001
Sex
 Boys1.0refref
 Girls0.860.72–1.010.018
Race
 White1.0refref
 Black1.451.10–1.930.001
No. of primaries
 1.01.0refref
 ≥2.01.790.93–3.450.022
Radiation
 Yes1.0refref
 No1.010.82–1.240.945
Cell type
 T-cell1.0refref
 B-cell, B-precursor0.720.59–0.88<0.0001

Notes and abbreviations. The significance level was 0.01. CI: confidence interval.
Cell type information is available since 1980 and for only total of 5988 patients (917 T-cell and 5071 B-cell/B-precursor). The proportion of B-cell/B-precursor increases precipitously over the year of diagnosis starting with 0.0% in 1980 to 89% in 2006. The above table illustrates an adjusted analysis with cell types restricting the sample size to 5988 patients. AHR: adjusted hazard ratio; ref: referent group.