Random sampling from databases: a survey

This paper reviews recent literature on techniques for obtaining random samples from databases. We begin with a discussion of why one would want to include sampling facilities in database management systems. We then review basic sampling techniques used in constructing DBMS sampling algorithms, e.g. acceptance/rejection and reservoir sampling. A discussion of sampling from various data structures follows: B ⁺ trees, hash files, spatial data structures (including R-trees and quadtrees). Algorithms for sampling from simple relational queries, e.g. single relational operators such as selection, intersection, union, set difference, projection, and join are then described. We then describe sampling for estimation of aggregates (e.g. the size of query results). Here we discuss both clustered sampling, and sequential sampling approaches. Decision-theoretic approaches to sampling for query optimization are reviewed.     

Pacification of Rio's Favelas and the “Pacification of the Pacification Police”: The Role of Coordinating Brokerage in Police Reform

Rio de Janeiro's drug dealer–dominated favelas are territories where the state lacks the monopoly of violence. They have historically been sites of sporadic and violent police operations. Rio's favela “pacification” program aimed to consolidate state control via the establishment of a Pacification Police Unit (UPP). This proximity policing program initially experienced mixed results in different “pacified” favelas. I take advantage of this state intervention at the urban margins to ask, what explains the positive reception of this policing initiative in some communities but not others? I concentrate my fieldwork in two communities sharing a UPP that represented extreme cases of success in terms of the program's reception by residents. I find that the coordinating brokerage of respected local organizations helps acculturate police to the community and minimize offensive police behavior, thereby “pacifying the Pacification Police.” Residents are receptive to these resocialized police who comply with local norms of respect. This police‐reforming brokerage is possible due to the high level of closure in the local network and due to a vibrant local community with a strong history of organizing. My findings emphasize the importance of considering the role of local civil society in police reform at the urban margins.     

The valuation “by-tranche” of composite investment instruments

The return on composite investment instruments takes the form of weighted-average, derived from two economic indicators or more. Three experiments illustrate that prospective investors tend to valuate composites “by-tranche”, consistently violating the premise of reduction. Valuation-by-tranche shows for uncertain and risky composites and reflects in allocation problems and binary choice. The willingness to invest still strongly increases when one tranche hedges against the other, suggesting that reduced-form considerations may interfere with the inclination to value by part. A hybrid model where investors weight the values of tranches, but also respond to the reduced-form, approximates the data most accurately.     

On Preference for Flexibility and Complexity Aversion: Experimental Evidence1

Desire for flexibility suggests that the value of a choice-menu should increase with the number of options included. Complexity-aversion on the other hand may imply that the value of a menu decreases with its cardinality. We present the results of an experiment where 5 groups of subjects were asked to evaluate saving plans that let the investor choose between alternative indexing-schemes before the saving period ends. The complexity of the different plans was manipulated in two ways: (1) increasing the number of indexing options; (2) reducing the quality of information upon which the choice between different indices is made. We show that an increase in the number of indexing-options produces a negative complexity effect when the quality of information is high. The same change however results in a positive flexibility effect when the quality of information is low. More generally our results suggest a `negative cross interaction of complexity effects' and that the impact of complexity is marginally decreasing. We discuss possible cognitive explanations to the observed evaluation-patterns. This revised version was published online in June 2006 with corrections to the Cover Date.     

A mixed integer programming and heuristic algorithm for a warehouses location problem

A warehouses location problem is treated using a mixed integer programming and a heuristic algorithm. A simplification of freight rates schedules, based upon shipments consolidation and a linear regression of rates vs distances was made. Warehousing costs were divided according to fixed and variable and related to the throughput of the warehouses. Consideration was given in the analysis to the choice between owning and leasing each warehouse. In the case studied, the analysis demonstrated that a possible saving of approximately 22 per cent in annual distribution costs could be realized under the optimized warehouse location network.     

Mother-infant emotional availability through the COVID-19 pandemic: Examining continuity,stability, and bidirectional associations

The COVID-19 pandemic may impact the development of infants' social communication patterns with their caregivers. The current study examined continuity, stability, and bidirectional associations in maternal and infant dyadic Emotional Availability (EA) before and during the COVID-19 pandemic. Participants were 110 Israeli mother-infant dyads (51% girls) that were assessed prior to (Mage = 3.5 months) and during (Mage = 12.4 months) the pandemic. At both time points, mother-infant interactions were observed during play (nonstressful context) and tasks designed to elicit infant frustration (stressful context). Maternal and child EA were coded offline. Maternal EA demonstrated no significant mean-level changes from before to during the COVID-19 pandemic, whereas infant responsiveness and involvement increased over time. Stability and bidirectional associations in EA differed by context and were evident only in the stressful context. Mothers' perceived levels of social support further moderated these associations. Specifically, infants' pre-pandemic responsiveness and involvement predicted maternal EA during the pandemic only when mothers reported low levels of social support. Our findings suggest that maternal and child EA were not adversely impacted by the COVID-19 pandemic. However, patterns of EA demonstrated moderate-to-no stability over time, suggesting considerable individual differences in trajectories of EA.     

Persons with disabilities and the Colombian armed conflict

This article is about the armed conflict in Colombia and the situation for people with disabilities. Decades of internal conflict have created a complex situation which both gives rise to disability but also fails to take account of the many urgent needs of people with disabilities. Despite the ratification by Colombia of the UN Convention on the Rights of Persons with Disabilities, persons with disabilities are still not accorded a voice in the peace agreements. Although there is little known about the extent of disability in Colombia, it is important to understand the history of the Colombian armed conflict to see how it impacts on disability issues. We conclude by highlighting the legal instruments in Colombia which provide opportunities now to redress some of those wrongs.     

The Making of a President: How Presidential Candidates Become Who They Are in Biographical Campaign Materials

This article examines how presidential campaigns claim that candidates became who they are by looking at biographical campaign materials through the lens of biographical reasoning. Biographical reasoning is the process of connecting the experiences in someone’s life to his or her identity, often by treating those experiences as either a cause or an illustration of characteristics. An analysis of biographical reasoning in presidential campaign materials from 1952 to 2016 reveals three key themes in how campaigns portray candidates’ development: (a) Early in life, candidates mostly acquire, rather than illustrate, positive characteristics; (b) candidates mostly improve as people without major characterological setbacks, going from good to better; and (c) candidates benefit very little from economic advantages. The consistency of these themes suggests that the conventions of biographical campaign materials include specific assumptions about how presidents should become who they are, some of which help campaigns connect candidates to important American myths.     

Stochastic models for greenhouse gas emission rate estimation from hydroelectric reservoirs: a Bayesian hierarchical approach

Herein, we propose a fully Bayesian approach to the greenhouse gas emission problem. The goal of this work is to estimate the emission rate of polluting gases from the area flooded by hydroelectric reservoirs. We present models for gas concentration evolution in two ways: first, by proposing them from ordinary differential equation solutions and, second, by using stochastic differential equations with a discretization scheme. Finally, we present techniques to estimate the emission rate for the entire reservoir. In order to carry out the inference, we use the Bayesian framework with Monte Carlo via Markov Chain methods. Discretization schemes over continuous differential equations are used when necessary. These models applied to greenhouse gas emission and Bayesian inference for this purpose are completely new in statistical literature, as far as we know, and contribute to estimate the amount of polluting gases released from hydroelectric reservoirs in Brazil. The proposed models are applied in a real data set and results are presented.