Table 1.

Sampling procedure in 5 cities of Hiroshima prefecture

City	Population	Proportion of population in each city	Required sample size*	Number of residents invited	Proportion of population invited
Total (5 cities in Hiroshima prefecture)	1,925,152	100%	5,680	7,500	0.39%
Hiroshima	1,196,138	62.1%	3,527	3,600	0.30%
Fukuyama	469,960	24.4%	1,386	1,400	0.30%
Higashi-Hiroshima	187,718	9.8%	557	1,000	0.53%
Miyoshi	53,556	2.7%	153	1,000	1.90%
Kita-Hiroshima	18,780	1.0%	57	500	2.66%

*Required total sample size was calculated assuming an antibody positivity rate of 0.20%, an absolute accuracy of 0.15%, and a participation rate of 60%. The required sample size for each city was determined by applying the required total sample size to the proportion of the population in each city.