## 3 Results and Discussions
### The Possibility of Promoting Respondent's U-Turn to Improve the Population Disparities  
The results above demonstrate that there are several groups of respondents (last nodes of the decision tree) who had different combinations of living environments as the components of their U-turn motivations. The respondents in each group had different demographic attributes. These results can assist in the construction of living environments or make policies in the regions that promote U-turn migration. Moreover, the results also indicate that the evaluation of several living conditions depends on the urban character of the respondents' hometowns or current places of residence, notably city size and geographical location. Our results aid in assessing the feasibility of U-turn migration in the current living conditions of each region, and in the new conditions after development. The results in Section 3.3 show that there are two groups of respondents for which U-turn motivation is high due to good environments in their hometowns, or poor environments in their current locales. However, it is arguable that unless people migrate from large population centers to less dense regions, the impact of improving population disparity will be small or negative. By contrast, in small hometowns for which potential returnees' U-turn motivations are low, if people's U-turn motivation is enhanced by solving problems through further development, their U-turn migration to these regions will contribute to improved population disparity. In this section, we assess this possibility of improving population disparity demonstrated by each respondent group in the decision tree. Furthermore, we recommend plans or policies for developing the regional living environments, which is necessary to improve the population disparity for the future regional sustainability. Table 9 shows the distribution ratio of (1) the city size of respondents' current residences, (2) the difference between city size of the hometown and place of current residence, and (3) the change in the region of residence in urban areas caused by their hypothetical U-turn. Based on these results, the notable characteristics of the hypothetical change after respondents' U-turn are summarized in Table 10.  
First, several respondents at Nodes 7 and 13 had high motivations toward U-turn migration. In addition, these nodes' branch conditions contained the living environments that have significant relationships with city features. More respondents (Node 7, 22.8%; Node 13, 27.3%) would migrate from provincial areas to the three major metropolitan areas if they conduct their U-turn migration. In addition, over half these respondents would migrate to larger cities with better shopping or transportation environments, which affects their U-turn motivations. The U-turn motivations of the respondents in these groups have the possibility of increasing, and not reducing, the population disparity, which is an undesirable outcome for Japan. It seems that preventing population outflow from current smaller cities and less populated areas is necessary. One solution is to develop the living environments of these respondents and develop their current places of residence to be more attractive. According to the results of the decision tree, these conditions include the transportation environment (Node 7), attachment to regions (Node 7), and pleasantness of climate (Node 13). A relationship was found between the evaluations for transportation environment and the city size. For Node 7, respondents' U-turn motivation was affected by the gap in this factor. However, the jurisdictions of the current residences of over 60% respondents were smaller than those of their hometowns. Therefore, for local governments in these regions must conduct assessments to and interventions to exceed the evaluations of the hometowns.