重新审视搜索摩擦下降、失业与增长

Federal Reserve Board, Washington, D.C.ISSN 1936-2854 (Print)ISSN 2767-3898 (Online) Declining Search Frictions, Unemployment, and Growth Revisited Juan Carlos C´ordoba, Anni T. Isoj¨arvi, Haoran Li 2025-098 Please cite this paper as:C´ordoba,Juan Carlos,Anni T.Isoj¨arvi,and Haoran Li(2025).“DecliningSearchFrictions,Unemployment,and Growth Revisited,”Finance and Economics DiscussionSeries2025-098.Washington:Board of Governors of the Federal Reserve System,https://doi.org/10.17016/FEDS.2025.098. NOTE: Staff working papers in the Finance and Economics Discussion Series (FEDS) are preliminarymaterials circulated to stimulate discussion and critical comment.The analysis and conclusions set forthare those of the authors and do not indicate concurrence by other members of the research staff or theBoard of Governors. References in publications to the Finance and Economics Discussion Series (other thanacknowledgement) should be cleared with the author(s) to protect the tentative character of these papers. Declining Search Frictions, Unemployment, and GrowthRevisited∗ Juan Carlos C´ordoba†Anni T. Isoj¨arvi‡Haoran Li§ October 21, 2025 Abstract This paper revisits the conditions under which search models generate balanced growth paths(BGPs)—equilibria where unemployment, vacancies, and job flows remain steady as searchfrictions decline. Martellini and Menzio (2020) claim that such paths exist only when matchesare “inspection goods” and match quality follows a Pareto distribution. We show that theseconditions are sufficient but not necessary. Their implementation assumes a strong form ofstationarity—requiring the endogenous distribution of match qualities to remain invariant underproportional scaling.This restriction forces the reservation quality to grow at a constant,strictly positive rate, mechanically tying declining frictions to long-term growth and yieldingcounterfactual implications of eliminating search frictions—persistent unemployment andinfinite welfare gains. Relaxing this restriction, balanced growth can arise under alternativeforms of scaling, such as additive transformations that restore stationarity without Paretotails or inspection. We further show that biased technological progress, when vacancies andunemployed workers are complementary inputs, also generates well-behaved BGPs with finitewelfare gains and vanishing unemployment as search frictions disappear. Keywords:search frictions; balanced growth; inspection models; Pareto tails; biased technologicalchange JEL Codes:E24; J64; O41 ”If search frictions in the labor market have diminished over the last 90 years, whydo we not see a secular inward shift of the Beveridge curve, a secular negative trendin the unemployment rate, and a secular rise in the UE rate?... We seek a balancedgrowth path (BGP) for this economy, that is, an equilibrium along which unemployment,vacancies, UE, and EU rates are constant over time... A BGP exist iff (a) the quality ofa firm-worker match is a sample from a Pareto distribution with some tail coefficient...and (b) the workers’ benefit from unemployment and the firms’ cost of maintaining avacancy grow at the same rate as average productivity. The assumption that matches areinspection goods could be considered the third condition for the existence of a BGP.”(Martellini and Menzio, 2020, pp. 4392). 1.Introduction Despite dramatic improvements in job-search technology over the past century—from newspaperclassifieds to online platforms to algorithmic matching—aggregate labor market outcomes haveremained remarkably stable. Unemployment rates show no secular decline, the Beveridge curvehas not shifted inward over the long run, and job-finding and separation rates appear stationary.This apparent disconnect between technological progress and stable labor-market outcomes poses afundamental puzzle for macroeconomic theory: how can declining search frictions coexist withsteady employment outcomes? Martellini and Menzio (2020) (hereafter MM) offer an influential answer. In the spirit of King,Plosser, and Rebelo (1988), they seek necessary and sufficient conditions for balanced growth insearch-theoretic models of unemployment. Their solution is strikingly sharp: a balanced growthpath exists if and only if firm–worker matches are “inspection goods” and match quality followsa Pareto distribution.1Under these assumptions, the long tail of the Pareto distribution inducesincreasingly selective matching that offsets the effects of declining frictions, thereby preserving thestability of labor market outcomes while generating long-run growth. This paper revisits and challenges that characterization. We show that MM’s conditions aresufficient but not necessary. The key lies in their implementation of the balanced-growth concept.In their definition—stated in the abstract and introduction—a BGP requires that aggregate laborvariables such as unemployment, vacancies, and job flows remain constant over time, but saysnothing about th