significant. Thus when all exposure cells within the males-Hiroshima cell are considered, the only evidence for an association of birthweight with parental exposure is the heterogeneity of the individual cell regressions. But, this association is neither consistent nor does it persist to a significant extent when the category 1 parents are excluded (see Table 10.5c).

Before we summarize and consider the possible interpretations of the findings on the males-Hiroshima data let us turn to the remaining three sex-city cells. Tables corresponding to those for males-Hiroshima are given for females-Hiroshima (Tables 10.9–10.13), males-

TABLE 10.8 THE RESIDUAL MEAN SQUARES FROMTHE INDIVIDUAL CELL REGRESSIONS: MALES, HIROSHIMA (The degrees of freedom are given in parentheses.)

			Mothers
			1	2	3	4–5
	1		1,747.87	1,649.29	1,768.00	1,595.93
			(8,669)	(2,711)	(1,061)	(537)
	2		1,777.14	1,783.05	1,738.38	1,876.84
			(740)	(894)	(215)	(104)
	3		1,849.41	1,957.12	1,798.85	1,764.54
			(291)	(186)	(252)	(44)
	4–5		2,382.73	1,968.26	1,598.47	1,609.30
			(195)	(110)	(73)	(51)
Bartlett's test for between-cell heterogeneity of mean squares:
		X2=20.43			DF=15
Bartlett's test for between-cell heterogeneity of mean squares when category 1 parents are excluded:
		X2=2.12			DF=8

Nagasaki (Tables 10.14–10.18) and females-Nagasaki (Tables 10.19–10.23). In none of these three sex-city cells does the analysis of variance on the adjusted data reveal significant differences as regards mean birthweight between maternal or paternal exposure categories or evidence of heterogeneity as judged by the interactions. In Table 10.24 are set out the principal findings with regard to the four sex-city cells. From this table when all exposure cells are considered we note (a) significant heterogeneity in the individual father-mother regressions in two of the four sex-city cells, (b) a reasonable measure of constancy in the amount of variation removed by the common regression in each sex-city cell, and (c) significant heterogeneity between the residual mean squares within a sex-

TABLE 10.9 ANALYSIS OF COVARIANCE OF BIRTHWEIGHTS: FEMALES, HIROSHIMA