Participants for the study in China were recruited from Shanghai and Jinan. Shanghai is the largest metropolitan city in China, with a population of 18.58 million people, 89% of which live in an urban area as Shanghai is a major financial, shipping, and industrial center. Jinan is the capital of Shandong province in northeast China and has a population of 6.6 million people, 71% of which live in an urban area as Jinan is characterized by heavy industry, textiles, and farm products, as well as service and information technology.
Participants were recruited from Medellín, in the Aburrá valley (located north of the Andes in South America), in the State of Antioquia, Colombia. Medellín is the second largest city in Colombia, after Bogotá and it has a population of 2,219,861. More than 80% of the city’s residents belong to the lower three of Colombia’s six official socioeconomic classes. These data are in agreement with national statistics attesting that about 10% of the Colombian population belong to the higher three of Colombia’s six official socioeconomic classes.
Participants were recruited in two sites: Rome and Naples. Rome is the capital of Italy and the country’s largest and most populated municipality, with more than 2.7 million residents. Rome is located in the central-western portion of the Italian Peninsula. The city has often been nicknamed Caput Mundi because it was the capital of the Roman Empire and it is the home of the Roman Catholic Church and of Vatican City, an independent city-state run by the Catholic Church. Rome is a cosmopolitan metropolis, and it is Italy’s capital of politics, economy, and media. Naples is the most important city in the south of Italy with a population of more than 1 million inhabitants in the city center and about 3 million in the suburbs. It is the third largest city in Italy in terms of population (after Rome and Milan) and occupies a central role in Southern Italy.
Participants were recruited from the city of Zarqa, which is located to the northeast of Jordan’s capital city of Amman. Zarqa has a population of 950,000 inhabitants comprising 15.5% of Jordan’s population; it is the country’s second largest city after Amman. The first settlement in Zarqa was in 1902 by Chechen immigrants who were displaced from the wars between the Ottoman and Russian Empires. They settled along the Zarqa River. At that time a station on the Hejaz railway was built in the new settlement; this railway station turned Zarqa into an important hub. On April 10, 1905, the Ottoman governor issued a decree that allowed Chechen immigrants to own lands on which they settled. The population then quickly grew. On November 18, 1928, the new Jordanian government issued a decree to establish the first municipal council for Zarqa. After the Jordan Frontier Force was formed in 1926, military bases were constructed in the city by the British army, and the city later became known as the “military city.” Migration to Zarqa has steadily progressed since the 1940s. More than 50% of Zarqa’s population migrated from the West Bank following the Six Day War. Zarqa’s climate is desert-like, to a much greater degree than nearby Amman. Zarqa is Jordan’s industrial center, home to over 50% of Jordanian factories. The growth of industry in the city is the result of low real estate costs and proximity to the capital, Amman.
Participants were recruited from Kisumu, Kenya. Kisumu is the third largest city in Kenya and a principal lake port located on the shores of Lake Victoria. The city began in 1901 as an inland terminal for the Kenya–Uganda railway. Since then, it has developed to become the provincial headquarters of Nyanza and a leading commercial, trading, industrial, and communication hub for the southwestern part of the country. It is accessible via a network of roads, railway, waterway, and an international airport. The majority of the inhabitants of Kisumu belong to the Luo ethnic group, and all participants in the study are members of this ethnic group. However, the city is also occupied by other ethnic communities including descendants of South East Asians brought in by the Imperial British East African Company to construct the Kenya–Uganda railway line.
Respondents were residents of Quezon City, the most populous and geographically largest city in metropolitan Manila. As the former capital, the city houses several major government institutions, prominent schools and universities, hospitals, business districts, and commercial shopping areas. Its 2.68 million residents (half of whom are below the age of 24) come from all socioeconomic strata.
Participants were recruited from Trollhättan and Vänersborg in the western part of Sweden. The population is 55,000 in Trollhättan and 37,000 in Vänersborg. In both cities, the inhabitants (between the ages of 30 and 49 years) have an average income of 262,000 Skr (about USD$40,000) a year, compared with individuals in the same age range in Sweden as a whole, who have an average income of 272,000 Skr (about USD$41,500) a year. Both of the cities are a part of the second largest county in Sweden, Västra Götalands län. The leading employer has been SAAB in Trollhättan, which makes the city an industrial town, whereas Vänersborg is known as a middle class town. In both cities, about 52% of the inhabitants have graduated from high school and 33% have studied at universities. Of 1–5-year-old toddlers, 80% attend preschool, and half of the children aged 6 to 12 years attend after-school centers. In Trollhättan, 16% of the population was born in another country and immigrated to Sweden, and in Vänersborg, 8% of the population are immigrants, compared to 14% in Sweden as a whole.
The community selected for recruitment of participants is in Chiang Mai, the Northern capital of Thailand with a population of 1.6 million. The majority of the population resides in and around the city center, which has seen rapid expansion during the last two decades. There are a large number of migrant workers from nearby areas, from the hill-tribe minority groups, and from neighboring countries who come to work in the city to support the tourist industry. As a result, Chiang Mai is a vibrant city replete with all kinds of amenities that make visiting and staying attractive to many. There are two large universities and one teachers’ college housing more than 20,000 students, 7 international schools, and over 30 regular schools ranging from elementary level to high school level, private and government run. Thus, many parents send their children to schools in Chiang Mai, many commute daily, and many more stay in numerous dormitories and apartment buildings.
Participants were recruited from Durham, North Carolina, in the United States of America. Durham is a city with a population of 250,000 located in a larger metropolitan area of North Carolina with a population of 1.2 million. North Carolina’s total population is 8.9 million. The leading employer in Durham is Duke University and Medical Center, but Durham was formerly a manufacturing hub in the tobacco industry and largely remains a working-class city. Of the population of Durham, 46% is European American, 11% is Latin American (although this number may be an underrepresentation given the undocumented Latin American families living in Durham), and 37% is African American. Of the Durham population, 14% is foreign born.