Table 15.

Risk of childhood cancer in twin cohorts^a,^b

Study, Yr Published, Location	Years of Birth	Number of Twins	Cancer		Relative Risk
			Observed	Expected
Hewitt D et al, 1966 United Kingdom	1943–63	Not provideda	121	152	0.80
Jackson EW et al, 1969, California	1940–64	145,708	100	110.6	0.90
Inskip PD et al, 1991, Connecticut	1930–69	30,925	31	46.4	0.67
Windham CC et al, 1985 Norway	1967–79	14,504	14	15.6	0.96
Rodvall Y et al, 1992, Sweden	1952–67	35,582	59	61.7	0.96

Source: Boice and Miller 1999 [17]

^aProportion undergoing pelvimetry x-rays was not determined, but range reported was 30–55%

^bData are based on the first 5,763 deaths included in the Oxford Survey of Childhood Cancers