We introduce a dynamical system to model the complex interaction between COVID-19 and economic activity. The model introduces some novelties not accounted by SIR-like models. The equilibrium of the system is an unstable focus, with fluctuations having increasing size and periodicity. Numerical simulations of the model produce waves which reproduce the pandemic dynamics. In observing the stylized facts linking economics and pandemic and stating related reasonable assumptions, we obtain a Lotka-Volterra co-dynamics. This outcome is confirmed by extensive simulations. The outcomes obtained qualitatively replicate some important stylized facts deepening the knowledge about the role of some parameters in their origin and eventually in their shaping.

This paper establishes the computational complexity status for a problem of deciding on the quality of a committee. Starting with individual preferences over alternatives, we analyse when it can be determined efficiently if a given committee [Formula: see text] satisfies a weak (resp. strong) Condorcet criterion-i.e., if [Formula: see text] is at least as good as (resp. better than) every other committee in a pairwise majority comparison. Scoring functions used in classic voting rules are adapted for these comparisons. In particular, we draw the sharp separation line between computationally tractable and intractable instances with respect to different voting rules. Finally, we show that deciding if there exists a committee which satisfies the weak (resp. strong) Condorcet criterion is computationally hard.

This paper concerns the ethical issues that arise when policy decisions have to be taken that affect population size and characteristics. Such policies include social security systems, intertemporal resource allocation decisions, and policies designed to influence fertility rates. The authors provide characterizations of Leximin principles for social evaluation in an intertemporal framework, so that they can be used to compare social alternatives with different population sizes. "The main axioms used in our characterizations are Hammond Equity together with Independence of the Utilities of the Dead (a plausible intertemporal consistency requirement) for the Critical-Level Leximin principles, and Positional Leximin Consistency (an axiom that allows non-constant critical levels) for the Positional-Extension Leximin principle. The performance of these principles is compared in the pure population problem and we argue that the Critical-Level Leximin principles are ethically more attractive than Positional-Extension Leximin."

This paper deals with some consequences of certain population changes on social welfare considerations. In particular, a general concept for expressing value judgments about how the addition of 1 further agent to some given society should affect social welfare and a replication invariance condition are introduced and discussed. An axiomatic framework for welfare orderings based on a generalized averaging procedure applied to individual utilities is provided.

The authors propose an economic model capable of simulating the 4 main historical stages of civilization: hunting, agricultural, industrial, and postindustrial. An output-maximizing society to respond to changes in factor endowments by switching technologies. Changes in factor proportions arise through population growth and capital accumulation. A slow rate of exogenous technical process is assumed. The model synthesizes Malthusian and Boserupian notions of the effect of population growth on per capita output. Initially the capital-diluting effect of population growth dominates. As population density increases, however, and a threshold is reached, the Boserupian effect becomes crucial, and a technological revolution occurs. The cycle is thereafter repeated. After the second economic revolution, however, the Malthusian constraint dissolves permanently, as population growth can continue without being constrained by diminishing returns to labor. By synthesizing Malthusian and Boserupian notions, the model is able to capture the salient features of economic development in the very long run.

"Eight independent pairs of entropy-based rankings of 3,140 U.S. county-level units are obtained. The criteria employed are the homogeneities of the distribution of 1965-70 in- and out-migrants of each county--for eight age-sex-specific groups--over the other 3,139 counties. The most homogeneous counties for males of ages 19-39 in 1970 consistently have major military facilities." The results show that "for those 65 and over, Florida, Arizona and Texas counties have the broadest in-migration, while Northern metropolitan counties have dispersed out-migration. The cross-correlations of entropies--though all strongly positive--are lowest between those 19-39 and those 65 and over, and relatively weak, in general, between those 65 and over and other groups. In all eight demographic groups, destination entropies reach higher values than origin entropies."