【Paper】　【Slide】

Abstract：Existing empirical research in economics on neighborhood racial sorting is overwhelmingly premised on the idea that racial preferences for a location depend on the racial shares in that location, without considering potential spatial spillover effects from nearby areas. Does this matter for the way we view the cross-section and dynamics of racial neighborhood segregation? We nest Schelling (1971)’s bounded neighborhood and spatial proximity theories within a discrete choice model, where the key distinction is precisely such spatial spillovers. We simulate the model and examine the data for 1970-2000 for more than 100 U.S. metros. Two features of the data are most compelling: the powerful presence of racial clusters and the fact that drastic racial change is concentrated at the boundary of these clusters. Both point to the spatial proximity model as the proper foundation for a theory of racial neighborhood evolution. We use these insights to revisit prominent results on racial tipping where our theory guides us to distinguish differences by location. While prior research pointed to powerful racial tipping in the form of White exit, we show this is largely driven by theoretically-distinct “biased white suburbanization” leading to White entry in remote areas. In urban areas far from existing Minority clusters, we find zero or small tipping effects, at odds with a bounded neighborhood interpretation. The most consistent effects of tipping, still of modest size, are found in areas adjacent to existing Minority clusters, confirming the relevance of the racial spillovers of the spatial proximity model. Existing research conflates these quite distinct effects. Overall, our results suggests that tipping is a less central feature of racial neighborhood change than suggested in prior research and that greater attention needs to be paid to spatial dimensions of the problem.

【参考資料】

Yoshifumi Konishi and Akari Ono, 2024, “Do Winners Win More from Transport Megaprojects? Evidence from the Great Seto Bridge in Japan.” Keio-IES Discussion Paper Series, DP2024-018.

要旨：Do industrial air pollution emissions become spatially dispersed or concentrated through investment in transportation infrastructure? What factors explain the spatial distribution of air pollution? To empirically investigate these questions, we develop a theoretical model consistent with insights from “Trade and the Environment” and “Quantitative Spatial Model”. Theoretically, we show that changes in air pollution can be expressed as a function of Market Access (MA) under heterogeneous environmental regulations and that these changes can be decomposed into scale, composition, and technique effects. To identify the causal effects, we exploit the substantial drop in transportation costs resulting from the construction of the Great Seto Bridge in western Japan during the 1980s and 1990s and construct an instrumental variable following the Recentered Approach. The estimation results indicate that changes in MA due to transportation investment lead to a reduction in ambient sulfur dioxide concentrations on average. Based on our theoretical model, we further examine whether there are heterogeneous effects on air pollution. Our analysis highlights that there are heterogeneous effects on industrial air pollution resulting from the pre-existing level of the MA variable and environmental regulations prior to transportation projects. This supports the spatial dispersion of air pollution through greater reductions in initially highly polluted areas.

【資料】（1/30更新）

要旨：有史以来、人間(ホモ・サピエンス)は都市を建設し、その都市は人口集中のるつぼであり続けてきた。都市は交易や統治の中心地でもあり、私たちに技術や文明や思想をもたらした半面、疫病の苗床として、収奪の拠点として、そしてストレスフルなライフスタイルを余儀なくされる空間でもあり続けた。このセミナー発表では、都市への人口集中がもたらす功と罪について、精神医学・進化生物学・社会学の観点から俯瞰したうえで、これからの人口集中・人口減少に際して乗り越えられるべき課題について議論を提示する。

Abstract：(Tentative) We draw on new granular data from cities around the world to study how the spatial distribution of income within cities varies with development. We document that in less-developed countries, average incomes of urban residents decline monotonically in distance to the city center, whereas income-distance gradients are flat or increasing in developed economies. We also show that urban neighborhoods with natural amenities – in hills and near rivers – are poorer than average in lessdeveloped countries and richer than average in developed ones. We hypothesize that these patterns arise due to the differences in the provision of residential and transportation infrastructure within cites. Using a quantitative urban model, we show that observed differences in residential and transportation infrastructure help explain a significant fraction of how the spatial income distribution within cities varies with income per capita.

要旨：本報告では、国立社会保障・人口問題研究所（社人研）で実施した「日本の地域別将来推計人口（令和5年推計）」（以下、「令和5年地域推計」）の推計手法を中心として、推計結果についても多少の説明を行う。将来人口推計は、基本的には過去～現在に観察された出生・死亡・人口移動の趨勢が将来も継続するという観点で行われている。地域別将来人口推計の場合、推計の肝となるのは人口移動に関する部分であり、これまで利用可能な統計等に合わせて移動数の推計方法の改良を行ってきた。「令和5年地域推計」では、仮定設定の基準となる期間を2005～2020年の5年ごと3期間として、2020～2025年に限定して新型コロナウイルス感染拡大の影響も考慮した移動仮定の設定を行った。推計結果からは、ほぼ全域的に人口減少がいっそう進展することが見て取れるが、人口学的にみた人口減少要因はほぼ自然減となる。少子化に伴う若年人口の減少によって、地方の社会減は限定的となる一方で、推計の基準時点（2020年）における人口構造が将来人口を大きく規定することになる。

要旨：本報告では、国立社会保障・人口問題研究所（社人研）で実施した「日本の将来推計人口（令和5年推計）」の推計手法と結果について報告する。前半では、公的推計の役割と方法論（人口投影という考え方、社会経済変数との関わり）、推計時点以降の年齢別人口の推計に必要な年齢別生残率の仮定（死亡仮定）、国際人口移動数（率）の仮定、そして、0歳人口の推計に必要な女性の年齢別出生率の仮定（出生仮定）の設定方法について説明する。後半では、2020年を基準人口とし、2070年まで推計された人口および年齢構成、人口動態数、日本人、外国人別の構成、機械的に仮定条件を変えた条件付き推計の結果を示す。前回推計よりも出生率仮定は低下するものの、平均寿命が延伸し、外国人の入国超過が増加することで、人口減少の進行はわずかに緩和される見込みとなった。出生中位（死亡中位）推計にもとづけば、2070年の日本は、総人口は現在の７割に減少し、65歳以上人口はおよそ４割を占め、外国人人口割合が1割を超える社会となる。

【論文】（10/09更新）

要旨：This paper investigates the elusive role of productivity heterogeneity in new trade models in the trade and environment nexus. We contrast the Eaton-Kortum and the Melitz models with firm heterogeneity to the Armington and Krugman models without heterogeneity. We show that if firms have a constant emission share in terms of sales — as they do in a wide range of trade and environment models — the three models’ emission predictions exactly coincide. Conversely, if firms have a constant emission intensity per quantity — a prominent alternative in the literature — the emission equivalence between the three models breaks. We provide a generalization that nests both constant emission shares in sales and constant quantity emission intensities as special cases. We calibrate the models to global production and trade data and use German firm-level data to estimate the key elasticity of how emission intensity changes with productivity. Our multi-industry quantification demonstrates that the role of firm heterogeneity depends both on the model and the estimated parameters. Moving from the Armington model to the EK model increases the emissions effect on trade, while moving from the Krugman model to the Melitz model decreases the emission effects on trade.