The WMH surveys were carried out in 10 countries classified by the World Bank20 as developed (Belgium, France, Germany, Israel, Italy, Japan, Netherlands, New Zealand, Spain, and United States) and 11 countries classified as developing (Brazil, Bulgaria, Colombia, India, Lebanon, Mexico, Nigeria, People’s Republic of China, Romania, South Africa, and Ukraine) (see Table 1). All surveys were conducted face-to-face by trained lay interviewers among multi-stage household probability samples and were completed between 2001 and 2007. The total sample size was 108,705, with individual country sample sizes ranging from 2,357 in Romania to 12,790 in New Zealand. The weighted average response rate across all countries was 73.0%.
