Table 1. Standardised incidence ratios (SIRs) for childhood acute lymphoblastic leukaemia associated with a family history of leukaemia.

Family history of	Obs.a	SIRsb (95% CI)
Any type of leukaemia (ICD c : 204–209), in:
Any first-degree relatives	19	2.21 (1.33–3.45)
Parents only	8	1.27 (0.55–2.50)
Siblings only	11	4.82 (1.70–12.20)
Siblings excluding twins	5	2.22 (0.51–7.32)
Twins	6	208.28 (54.05–641.09)
Acute lymphoblastic leukaemia (ICD 204.0), in
Any first degree relatives	14	3.80 (2.08–6.38)
Any first-degree relatives excluding twins	8	2.18 (0.94–4.30)
Myeloid leukaemia (ICD 205), in
Any first degree relatives	4	1.25 (0.34–3.20)
Any first-degree relatives excluding twins	4	1.25 (0.34–3.20)

^aObserved number of cases.

^bSIRs stratified by age and follow-up period.

^cInternational Classification of Disease.