Search results for "Heterogeneity."
showing 10 items of 388 documents
Revisiting the role of top-down and bottom-up controls in stabilisation of nutrient-rich plankton communities
2019
Understanding the conditions for successful control of phytoplankton by zooplankton in eutrophic ecosystems is a highly important research area with a wide implementation of mathematical modelling. Theoretical models generally predict destabilisation of food webs in eutrophic environments with large-amplitude oscillations of population densities which would eventually result in species extinction. On the other hand, these theoretical predic- tions are often at odds with ecological observations demonstrating stable dynamics even for a high nutrient load. This apparent discrepancy is known in the literature as Rosen- zweig’s “paradox of enrichment”. Recent theoretical works emphasize a crucia…
Small Mammals in Forests of Romania: Habitat Type Use and Additive Diversity Partitioning
2021
Small mammals are key components of forest ecosystems, playing vital roles for numerous groups of forest organisms: they exert bottom-up and top-down regulatory effects on vertebrate and invertebrate populations, respectively
Does Tourism Consumption Behaviour Mirror Differences in Living Standards?
2016
Based on the theoretical foundation of well-being measurement, the study explores differences in living standards by analysing the distribution of tourism expenditure. A mixture of regression models is used to explore the heterogeneity in tourism consumption by identifying groups of families with similar tourism consumption behaviour as a function of certain socio-demographic and economic factors. The empirical analysis, performed on Italian expenditure data, suggests that there are three different patterns of consumption behaviour conditional to the socio-demographic and economic covariates in the tourism market and that differences in tourism consumption between groups of households mirro…
Unbundling technology adoption and tfp at the firm level. Do intangibles matter?
2012
We use a panel of European firms to investigate the relationship between intangible assets and productivity. We distinguish between total factor productivity (tfp) and technology adoption, whereas standard estimations consider only a notion of productivity that conflates the two effects. Although we are unable to address simultaneity, we allow for the existence of multiple technologies within sectors through a mixture model approach. We find that intangible assets have nonnegligible effects that both push firms toward better technologies (technology adoption effects) and allow for more efficient exploitation of a given technology (tfp effects).
The welfare cost of unpriced heterogeneity in insurance markets
2016
We consider the welfare loss of unpriced heterogeneity in insurance markets, which results when private information or regulatory constraints prevent insurance companies to set premiums reflecting expected costs. We propose a methodology which uses survey data to measure this welfare loss. After identifying some “types” which determine expected risk and insurance demand, we derive the key factors defining the demand and cost functions in each market induced by these unobservable types. These are used to quantify the efficiency costs of unpriced heterogeneity. We apply our methods to the US Long-Term Care and Medigap insurance markets, where we find that unpriced heterogeneity causes substan…
School grading and institutional contexts
2011
We study how the relationship between students' cognitive ability and their school grades depends on institutional contexts. In a simple abstract model, we show that unless competence standards are set at above-school level or the variation of competence across schools is low, students' competence valuation will be heterogeneous, with weaker schools inflating grades or flattening their dependence on competence, therefore reducing the information content and comparability of school grades. Using data from the OECD-PISA 2003 Survey, the model is applied to a sample of four countries, namely Australia, Germany, Italy, and the Netherlands. We find that in Australia, schools' heterogeneity does …
The democratization process: An empirical appraisal of the role of political protest
2020
Abstract This paper analyses the role of peaceful and violent protest in the democratization process. We interpret the democratization process as a sequence of phases so as to allow citizens' and elites' preferences for democracy to vary according to the particular phase that a country is experiencing. By doing so we jointly model the probability of protest and of moving through different phases of democracy taking into account time-constant and time-varying unobserved heterogeneity. In particular, we develop a multivariate finite mixture model that introduces a latent variable to capture unobservable factors. On a sample of 171 countries from 1971 to 2010, we provide evidence that protest …
Does one size fit all? The impact of cognitive skills on economic growth
2016
Les Documents de Travail de l'IREDU, n°2016-1; This paper tests for heterogeneous effects of cognitive skills on economic growth across countries. Using a new extended dataset on cognitive skills and controlling for potential endogeneity, we find that the magnitude of the effect is about 60 per cent higher for low-income countries compared to high-income countries, and it more than doubles when low TFP countries are compared to high TFP countries. There are also marked differences across geographic regions. Using data on the share of the population with advanced and minimum skill levels, our results also indicate that high-income countries should focus on increasing the number of high skill…
Establishment size and task-specific wages: Evidence from historical contract data
2014
This study examines whether task-specific jobs are rewarded differently across establishments of different sizes and whether these rewards vary across distinct technologies. We found that the aggregate premium estimates on the impact of size on wages conceal significant differences between tasks and technologies and that these differences reflect unobserved individual heterogeneity. The role of self-selection of more productive workers into larger establishments is particularly substantial in the case of abstract tasks. peerReviewed
Heterogeneous effects of sustainable agriculture practices: micro-evidence from Malawi
2020
Abstract Are the effects of sustainable agricultural practices heterogeneous across agro-ecology and wealth in Malawi? Would a wealth-enhancing policy be associated with increased effectiveness of these practices? Focusing on a nationally representative set of Malawian agricultural households, the article answers the above questions by employing plot-level panel data matched with a set of geo-referenced rainfall and temperature records. The findings suggest a positive correlation between aggregate yield and the adoption of organic fertilizer. A similar result holds for legume intercropping and for hybrid seeds, which are associated to reductions in yield volatility between the two waves. Ne…