Table 3.

Estimate of bladder cancer cases potentially attributable to chlorination DBPs among U.S. community water systems in year 2011 post-Stage 1 D/DBPR and any year post-Stage 2 D/DBPR (see Excel Table S3 for underlying data).

Source water type	System size (population served)	OR		PAR		Number of annual cases attributable to DBPs
		$\le 40\mathrm{\mu }\mathrm{g}/\mathrm{L}$	$>40–80\mathrm{\mu }\mathrm{g}/\mathrm{L}$	$\le 40\mathrm{\mu }\mathrm{g}/\mathrm{L}$	$>40–80\mathrm{\mu }\mathrm{g}/\mathrm{L}$	$\le 40\mathrm{\mu }\mathrm{g}/\mathrm{L}$	$>40–80\mathrm{\mu }\mathrm{g}/\mathrm{L}$	Total
Surface water systems–post-Stage 1a	$<\mathrm{10,000}$	1.1009	1.2631	0.27%	0.80%	212	635	847
	10,000–100,000	1.1061	1.2510	1.37%	1.91%	1,080	1,510	2,590
	$>\mathrm{100,000}$	1.1051	1.2347	2.23%	3.12%	1,770	2,470	4,230
	Subtotal	1.1052	1.2434	3.79%	5.64%	3,060	4,610	7,670
Groundwater systems–post-Stage 1a	$<\mathrm{10,000}$	1.0272	1.2725	0.24%	0.27%	186	215	401
	10,000–100,000	1.0479	1.2583	0.44%	0.41%	352	321	673
	$>\mathrm{100,000}$	1.0728	1.2407	0.30%	0.11%	248	85	333
	Subtotal	1.0445	1.2603	0.99%	0.78%	786	621	1,410
All systems–post-Stage 1a	Total	1.0821	1.2452	4.68%	6.34%	3,850	5,240	9,080
Surface water systems–post-Stage 2b	$<\mathrm{10,000}$	1.1009	1.2273	0.27%	0.70%	212	549	761
	10,000–100,000	1.1061	1.2049	1.37%	1.57%	1,080	1,240	2,320
	$>\mathrm{100,000}$	1.1052	1.1933	2.23%	2.59%	1,770	2,040	3,810
	Subtotal	1.1052	1.2011	3.79%	4.71%	3,060	3,830	6,890
Groundwater systems–post-Stage 2b	$<\mathrm{10,000}$	1.0272	1.2311	0.24%	0.23%	186	183	369
	10,000–100,000	1.0479	1.2458	0.45%	0.39%	352	306	658
	$>\mathrm{100,000}$	1.0728	1.2252	0.31%	0.10%	248	79	327
	Subtotal	1.0445	1.2379	0.99%	0.72%	786	568	1,350
All systems–post-Stage 2b	Total	1.0821	1.2051	4.68%	5.36%	3,850	4,400	8,240

Note: Estimates on this table reflect rounding. Example calculation for OR, PAR, and number of cases [shown for post-Stage 1, surface water systems serving $>\mathrm{100,000}$ people and with a population-weighted THM4 mean of $49.4\mathrm{\mu }\mathrm{g}/\mathrm{L}$ (see Table 2)]: $\text{OR}={\mathrm{e}}^{49.4\times 0.00427}=1.2347$. Fraction of $\text{Total\hspace{0.17em}Population}=42.3\text{\hspace{0.17em}million}/308\text{\hspace{0.17em}million}=0.1373$. $\text{PAR}=0.1373\times \left(1.2347-1\right)1\hspace{0.17em}+\hspace{0.17em}\left[0.1373\times (1.2347-1)\right]=0.0312=3.12\%$. $\text{Number\hspace{0.17em}of\hspace{0.17em}cases}\hspace{0.17em}=\hspace{0.17em}0.0312\times \mathrm{79,030}=\mathrm{2,467}$ (shown in Table 3 as 2,470 due to rounding). DBP, disinfection byproducts; D/DBPR, U.S. Environmental Protection Agency Disinfectants and Disinfection Byproducts Rule; OR, odds ratio; PAR, population attributable risk; THM4, trihalomethane-4; U.S. EPA, U.S. Environmental Protection Agency.

^a Stage 1 U.S. EPA Disinfectants and Disinfection Byproducts Rule.

^b Stage 2 U.S. EPA Disinfectants and Disinfection Byproducts Rule.