Natural experiment | EPFL Graph Search

A natural experiment is a study in which individuals (or clusters of individuals) are exposed to the experimental and control conditions that are determined by nature or by other factors outside the control of the investigators. The process governing the exposures arguably resembles random assignment. Thus, natural experiments are observational studies and are not controlled in the traditional sense of a randomized experiment (an intervention study). Natural experiments are most useful when there has been a clearly defined exposure involving a well defined subpopulation (and the absence of exposure in a similar subpopulation) such that changes in outcomes may be plausibly attributed to the exposure. In this sense, the difference between a natural experiment and a non-experimental observational study is that the former includes a comparison of conditions that pave the way for causal inference, but the latter does not. Natural experiments are employed as study designs when controlled e

"Immigration, Innovation, and Knowledge Diffusion"

Gabriele Cristelli

This dissertation studies the relationship between immigration and innovation. It adopts an empirical perspective and focuses on Switzerland, combining the use of patent data and immigration administrative records. The first essay is based on a novel database on immigrant inventors and explores their role in Swiss R&D activities, their productivity, and inventive career before and after immigration. It shows that highly productive inventors are over-represented among immigrants and that foreign inventors tend to enter Switzerland early in their careers and with little prior inventive experience. The second essay studies the innovation effects of the Agreement on the Free Movement of Persons (AFMP), which lifted immigration restrictions for EU citizens to Switzerland after its introduction in 2002. It exploits a natural experiment generated by regional differences in the exposure to the AFMP and influx of foreign workers. It finds that the AFMP introduction increased regional patenting in Switzerland and did not depress the inventive output of its neighbouring countries. In addition, Swiss inventors did not reduce their inventive activity due to newly arrived foreigners. Further results show that the AFMP had a positive effect on incumbent inventors' productivity, increasing the number of foreign collaborators and the variety of technical knowledge available.The third essay also focuses on the AFMP and studies the effects of the Swiss and the German labor markets' integration on technical knowledge diffusion. Using patent citation data and textual similarity measures, it demonstrates that the abolition of immigration restrictions for commuters residing in the German state of Baden-Wuerttemberg and working in Switzerland increased the diffusion of German inventions patented in commuters' residential locations into Switzerland.

EPFL2021

Four-dimensional distribution of the 2010 Eyjafjallajokull volcanic cloud over Europe observed by EARLINET

Ivan Videnov Grigorov, Valentin Mitev, Ilya Serikov, Valentin Simeonov, Frank Rüdiger Wagner, Xiao Wang

The eruption of the Icelandic volcano Eyjafjallajokull in April-May 2010 represents a "natural experiment" to study the impact of volcanic emissions on a continental scale. For the first time, quantitative data about the presence, altitude, and layering of the volcanic cloud, in conjunction with optical information, are available for most parts of Europe derived from the observations by the European Aerosol Research Lidar NETwork (EARLINET). Based on multi-wavelength Raman lidar systems, EARLINET is the only instrument worldwide that is able to provide dense time series of high-quality optical data to be used for aerosol typing and for the retrieval of particle microphysical properties as a function of altitude. In this work we show the four-dimensional (4-D) distribution of the Eyjafjallajokull volcanic cloud in the troposphere over Europe as observed by EARLINET during the entire volcanic event (15 April-26 May 2010). All optical properties directly measured (backscatter, extinction, and particle linear depolarization ratio) are stored in the EARLINET database available at www.earlinet.org. A specific relational database providing the volcanic mask over Europe, realized ad hoc for this specific event, has been developed and is available on request at www.earlinet.org. During the first days after the eruption, volcanic particles were detected over Central Europe within a wide range of altitudes, from the upper troposphere down to the local planetary boundary layer (PBL). After 19 April 2010, volcanic particles were detected over southern and south-eastern Europe. During the first half of May (5-15 May), material emitted by the Eyjafjallajokull volcano was detected over Spain and Portugal and then over the Mediterranean and the Balkans. The last observations of the event were recorded until 25 May in Central Europe and in the Eastern Mediterranean area. The 4-D distribution of volcanic aerosol layering and optical properties on European scale reported here provides an unprecedented data set for evaluating satellite data and aerosol dispersion models for this kind of volcanic events.

Copernicus Gesellschaft Mbh2013

How Anticipated Employee Mobility Affects Acquisition Likelihood: Evidence from a Natural Experiment

Kenneth Younge

This study draws on strategic factor market theory and argues that acquirers' decisions regarding whether to bid for a firm reflect their expectations about employee departure from the firm post-acquisition, suggesting a negative relationship between the anticipated employee departure from a firm and the likelihood of the firm becoming an acquisition target. Using a natural experiment and a difference-in-differences approach, we find causal evidence that constraints on employee mobility raise the likelihood of a firm becoming an acquisition target. The causal effect is stronger when a firm employs more knowledge workers in its workforce and when it faces greater in-state competition; by contrast, the effect is weaker when a firm is protected by a stronger intellectual property regime that mitigates the consequences of employee mobility.

Wiley-Blackwell2015

Four-dimensional distribution of the 2010 Eyjafjallajokull volcanic cloud over Europe observed by EARLINET

Ivan Videnov Grigorov, Valentin Mitev, Ilya Serikov, Valentin Simeonov, Frank Rüdiger Wagner, Xiao Wang

Copernicus Gesellschaft Mbh2013