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.

要旨：This study examines the impacts of eliminating school zones, focusing on the commuting behavior of high school students. To address this issue, we exploit the reform of the education system of public high schools in Nagasaki City, Japan. Before the reform in 2002, the local government assigned students to equalize the educational level among schools. While the reform enabled the students to choose a school on their own, the gap in academic performance among schools has widened. We found that one possible reason for this gap is the concentration of students from highly educated areas to schools with location advantages regarding transport accessibility and urban amenities.

【Paper】

Abstract: We explore the impact of public school assignment reforms by building a households’ school choice model with two key features—(1) endogenous residential location choice and (2) opt-out to outside schooling options. Households decide where to live taking into account that locations determine access-to-school—admissions probabilities and commuting distances to schools. Households are heterogeneous both in observed and unobserved characteristics. We estimate the model using administrative data from New York City’s middle school choice system. Variation from a boundary discontinuity design separately identifies preferences for access-to-school from other location amenities. Residential sorting based on access-to-school preference explains 30% of the gap in test scores of schools attended by minority students versus their peers. If households’ residential locations were fixed, a reform that introduces purely lottery-based admissions to schools in lower- and mid-Manhattan would reduce the cross-racial gap by 7%. However, households’ endogenous location choices dampen the effect by half.

要旨：Japan’s economy faces the challenges of demographic aging, with the aging of CEOs being a significant channel. When a CEO cannot find a successor, the firm may be forced to voluntarily exit the market. This study examines the propagation effects of demographic aging by analyzing the correlation between the voluntary exits of firms and their business partners. We hypothesize that the voluntary exit of a firm could lead to the voluntary exit of its business partners, creating a cascading effect throughout the firm network. Using firm-level data and controlling firm characteristics, industry, and year fixed effects, we find a positive and significant correlation between the voluntary exits of owned firms and their business partners. Furthermore, we observe that these effects are more pronounced for firms located in peripheral prefectures, possibly due to lower firm density and diversity, making it harder for firms to find new business partners after the exit of an existing one. This difference between core and peripheral prefectures is particularly strong for linkages between manufacturing firms , which can be attributed to input specificity. Our findings contribute to understanding the impact of demographic aging on firm networks and have implications for industrial policies aimed at maintaining the viability of firms, especially in peripheral areas.