3.1. Materials

The data used in this study were retrieved from two open datasets about the perceptions of air pollution among inhabitants of Hanoi [52,53]. These datasets are the results of two survey collections using stratified random sampling methods conducted in the central and suburban areas of the city, respectively. The data were collected during November and December 2019. Hanoi was chosen as the study site due to three reasons: (1) Hanoi was ranked 7th among the most polluted capital cities around the world [5]; (2) Hanoi is a fast-growing city in Vietnam; and (3) Hanoi is the second largest and most populous city in Vietnam.

Normally, migrants are attracted to growing big cities for better job opportunities [54,55]. However, the accumulation of anthropogenic activities in such cities (e.g., traffic, construction) can result in air pollution, which can possibly lead to averting behaviors and intentions through internal migration. Hanoi’s city features make it representative of other urban areas, not only in Vietnam, but also in other developing countries with similar socio-demographic characteristics for studying the underlying psychological mechanism of internal migration.

According to Khuc, Phu and Luu [53], the survey collection consisted of three steps. First, the collectors were recruited and paid to encourage them to perform well during the collection process. The researchers also held two four-hour seminars to help the collectors understand the project’s goals and the questionnaire’s content. During the seminar, necessary skills and techniques to extract information from respondents were also discussed. Then, two pilot tests were conducted to ensure the final version was error-free, straightforward, and easy to understand. Lastly, the collectors conducted face-to-face interviews with the respondents and maintained mutual interaction and communication to solve issues or answer questions arising during the survey collection. There was a total of 475 respondents, of which the majority were in the age group of 19–40 (52.84%). Male respondents accounted for 54.53% of the total respondents, while female respondents accounted for 45.26%. Among 475 respondents, approximately 10% reported their intention to move to another province/city to live and work due to air pollution in their current places. See Table A1 in the Appendix A for more descriptive statistics.

Following the conceptual models explained in the Theoretical Foundation section, we generated seven variables to be used for Bayesian analysis: six predictor variables and one outcome variable (see Table 1).

The outcome variable is MigratIntention, created from the question, “Do you intend to move your family and work in another province/city with less pollution?” Two answers are possible: ‘yes’ and ‘no’.

The urban people’s satisfaction with the current air quality level is determined by asking, “Overall, how satisfied are you with the air quality?”, and demonstrated by the AirSatisfaction variable. The air satisfaction level is rated on a four-point Likert scale ranging from one (‘very dissatisfied’) to four (‘very satisfied’).

NearbyMigratOpt and FarawayMigratOpt variables were modified from two original items in the dataset. Originally, Khuc, Phu and Luu [53] asked the respondents, “How do you feel about the air quality in Hanoi compared to neighboring provinces/cities?” and “How do you feel about the air quality in Hanoi compared to southern provinces/cities?” Four answers were possible: ‘better than’, ‘same as’, ‘less than’, and ‘I don’t know’.

While the NearbyMigratOpt variable is an unambiguous indication of nearby availability of provinces/cities with better air quality, the variable, FarawayMigratOpt, needs some contextual knowledge to comprehend. Specifically, Ho Chi Minh City and Hanoi are the two largest cities in Vietnam. While Hanoi is the capital city in North Vietnam, Ho Chi Minh is the largest city in the South, which is 1137 km away from Hanoi. In Vietnam, people usually use ‘the North’ to indicate Hanoi and its nearby provinces/cities, and ‘the South’ to indicate Ho Chi Minh city and its surrounding provinces/cities [56,57]. Despite being in the same country, these two regions have some distinct cultural characteristics due to the complex cultural change and historical events [58]. Given the distance and some socio-cultural differences between Hanoi and the South of Vietnam, it is plausible to use the variable FarawayMigratOpt to represent the perceived faraway options with better air quality. In addition, for investigating the impact of perceived option availability, modifications were made to turn them into binary variables, with one being ‘less than’, and zero being ‘better than’ and ‘same as’. The respondents that reported ‘I don’t know’ were excluded from the analysis.