Table 4 Descriptive statistics and results of variance ratio (F_max) test for shigella incidence under various neighborhoods, Nha Trang, Vietnam, 1999–2001. (n = 13565)

r ^†	Population size			Incidence Rate/10000 Population				Upper F_max Test			Lower F_max Test
	Min	Max	Mean	Min	Max	Mean	Variance	F_max1	DF₁ *	CV₁ **	F_max2	DF₂ *	CV₂ **
100	3	5692	1015	.00	333.30	6.041	197.436	25.397	20	1.571	1.000	1	3.842
200	3	17440	3223	.00	333.30	6.155	74.927	9.638	19	1.587	2.635	2	2.996
300	3	25689	6026	.00	57.14	6.112	38.808	4.992	18	1.605	5.088	3	2.606
400	10	34531	9388	.00	41.67	6.116	28.304	3.641	17	1.624	6.976	4	2.373
500	30	47539	13112	.00	57.47	6.102	22.808	2.934	16	1.644	8.656	5	2.215
600	33	61692	17105	.00	34.36	6.121	18.871	2.427	15	1.667	10.462	6	2.099
700	33	73490	21480	.00	35.46	6.129	16.566	2.131	14	1.692	11.918	7	2.010
800	87	88015	26126	.00	27.47	6.140	14.514	1.867	13	1.721	13.603	8	1.939
900	87	102106	30938	.00	22.87	6.148	13.374	1.720	12	1.753	14.763	9	1.881
1000	87	111244	35834	.00	31.15	6.158	12.651	1.627	11	1.789	15.606	10	1.831
1100	87	121667	40711	.00	19.67	6.137	11.774	1.515	10	1.831	16.769	11	1.789
1200	150	134222	45547	.00	18.28	6.116	11.057	1.422	9	1.881	17.856	12	1.753
1300	425	146883	50410	.00	17.64	6.119	10.536	1.355	8	1.939	18.739	13	1.721
1400	628	152901	55270	.00	16.40	6.135	10.079	1.297	7	2.010	19.589	14	1.692
1500	628	156963	60090	1.21	15.92	6.135	9.588	1.233	6	2.099	20.592	15	1.667
1600	628	161121	64829	1.77	15.92	6.123	9.104	1.171	5	2.215	21.687	16	1.644
1700	628	165020	69457	1.21	15.92	6.129	8.751	1.126	4	2.373	22.562	17	1.624
1800	628	170190	74078	2.73	15.92	6.135	8.411	1.082	3	2.606	23.474	18	1.605
1900	628	177965	78890	2.68	15.92	6.153	8.099	1.042	2	2.996	24.378	19	1.587
2000	628	182551	83821	2.98	15.92	6.171	7.774	1.000	1	3.842	25.397	20	1.571

^† r = size of neighborhood in meter radius
* DF = degrees of freedom
**CV₁ and CV₂ = critical values at 95% confidence level for Upper F_max and Lower F_max respectively Bold figures in F_max1 and F_max2 are the upper and lower limit of optimal neighborhoods, and the bold figure in "r" column is the choice of optimal neighborhood size.

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