Relationship between different sources of drinking water, water quality improvement and gastric cancer mortality in Changle County - A retrospective-cohort study in high incidence area

Table 3 Improved water and gastric cancer mortality rates for seven towns in Changle County (1/10⁵)

	Male			Female			Total
	Person-year observed	No. of deaths	Death rate	Person-year observed	No. of deaths	Death rate	Person-year observed	No. of deaths	Death rate
Persistent river water supply	37484	43	114.72	36856	12	32.56	74340	55	73.98
River water changed to tap water	35088	14	39.90	24262	4	16.49	59350	18	30.33
RR		0.35			0.51			0.41
χ2		12.93			1.44			11.52
P		0.0003b			0.2295			0.0007b
Persistent well water supply	411547	355	86.26	362687	118	35.23	774234	473	61.10
Well water changed to tap water	10449	3	28.71	8711	2	22.96	19160	5	26.10
RR		0.33			0.71			0.43
χ2		3.98			0.24			3.80
P		0.0460a			1.0000			0.0512a

^aP < 0.05,

^bP < 0.01.