Sampling from spatial databases

This paper deals with techniques for obtaining random point samples from spatial databases. We seek random points from a continuous domain (usually ²) which satisfy a spatial predicate that is represented in the database as a collection of polygons. Several applications of spatial sampling (e.g. environmental monitoring, agronomy, forestry, etc) are described. Sampling problems are characterized in terms of two key parameters: coverage (selectivity), and expected stabbing number (overlap). We discuss two fundamental approaches to sampling with spatial predicates, depending on whether we sample first or evaluate the predicate first. The approaches are described in the context of both quadtrees and R-trees, detailing the sample first, acceptance/rejection tree, and partial area tree algorithms. A sequential algorithm, the one-pass spatial reservoir algorithm is also described. The relative performance of the various sampling algorithms is compared and choice of preferred algorithms is suggested. We conclude with a short discussion of possible extensions.     

Dynamic reasoning and time pressure: Transition from analytical operations to experiential responses

Based upon the Decision Field Theory (Busemeyer and Townsend 1993), we tested a model of dynamic reasoning to predict the effect of time pressure on analytical and experiential processing during decision-making. Forty-six participants were required to make investment decisions under four levels of time pressure. In each decision, participants were presented with experiential cues which were either congruent or incongruent with the analytical information. The congruent/incongruent conditions allowed us to examine how many decisions were based upon the experiential versus the analytical information, and to see if this was affected by the varying degrees of time pressure. As expected, the overall accuracy was reduced with greater time pressure and accuracy was higher when the experiential and analytical cues were congruent than when they were incongruent. Of great interest was the data showing that under high time pressure participants used more experiential cues than at other time pressures. We suggest that the dynamic reasoning paradigm has some future potential for predicting the effects of experiential biases in general, and specifically under time pressure.     

The Collapsing Choice Theory: Dissociating Choice and Judgment in Decision Making

Decision making theory in general, and mental models in particular, associate judgment and choice. Decision choice follows probability estimates and errors in choice derive mainly from errors in judgment. In the studies reported here we use the Monty Hall dilemma to illustrate that judgment and choice do not always go together, and that such a dissociation can lead to better decision-making. Specifically, we demonstrate that in certain decision problems, exceeding working memory limitations can actually improve decision choice. We show across four experiments that increasing the number of choice alternatives forces people to collapse choices together, resulting in better decision-making. While choice performance improves, probability judgments do not change, thus demonstrating an important dissociation between choice and probability judgments. We propose the Collapsing Choice Theory (CCT) which explains how working memory capacity, probability estimation, choice alternatives, judgment, and regret all interact and effect decision quality.      

To be or not to be: the effects of aging stereotypes on the will to live

This study examined whether stereotypes of aging might contribute to decisions the elderly make about when to die. Old and young participants (N=64) were subliminally primed with either negative or positive stereotypes of old age and then responded to hypothetical medical situations involving potentially fatal illnesses. Consistent with our prediction, the aged participants primed with negative stereotypes tended to refuse life-prolonging interventions, whereas the old participants primed with positive age stereotypes tended to accept the interventions. This priming effect did not emerge among the young participants for whom the stereotypes were less relevant. The results suggest that societally-transmitted negative stereotypes of aging can weaken elderly people's will to live.     

Modelling state anxiety in a medical setting: The mediating role of embarrassment

Abstract

Little research has been conducted on the relationship between state anxiety and embarrassment in a medical setting. In the prcsent study, several personality and situational variables were examined as antecedents of state anxiety. A total of 277 patients who had come for an examination either as a response to a melanoma screening programme or due to a dermatological complaint participated in the study. Results showed that purpose of patient visit, physician's recommendation, trait anxiety, and embarrassment, were each correlated with state anxiety. Furthermore, using mediated regression analysis as well as structural equations, embarrassment was found to mediate between the above antecedents and state anxiety. The authors proposed a model linking all the variables and identifying their paths. Theoretical and practical considerations of the findings are discussed.     

Out‐of‐Home Placement of Children Exposed to Violence

There is growing concern about the increasing number of children in the USA who are exposed to community violence and the need to remove some of them from their families. This study examines risk factors for out‐of‐home placement among a large pool of children and adolescents who were referred for general clinical assessment following exposure to violence and/or psychological trauma in their communities or homes. Children with greater familial and environmental support and children exposed to incidents involving a non‐parental personal threat were associated with a significantly lower risk of out‐of‐home placement. A greater likelihood of being placed out of home was associated with older age (adolescents), history of mental health service use, involvement with law enforcement agencies, higher clinical ratings of depression or impaired thought processes, lower clinical functioning and greater exposure to traumatic events. Evidence of maltreatment and a threat to life was associated with 13.6 times greater likelihood of being placed out of the home. This study raises an important issue in respect to the children's past use of mental health service and current symptoms. It is not just the risk of violence but also evidence of psychiatric problem that trigger out‐of‐home placement. Further studies are needed to assess the quality and effectiveness of mental health services provided to children exposed to violence. © 2007 The Author(s). Journal compilation © 2007 National Children's Bureau.     

Population viability assessment and sensitivity analysis as a management tool for the peri-urban environment

Anthropogenic disturbance occurring within urban ecosystems is often extreme and highly variable. A quantifiable measure of their effect on the persistence of urban wildlife populations would contribute to conservation efforts. This study suggests that population viability assessment, a commonly utilized modeling tool for creating management strategies for rare and threatened wildlife populations, is also appropriate in an urban context. It can be used to create proactive management strategies that quantify the impacts of anthropogenic disturbances and rank a range of management options within an active adaptive framework. To show this, population viability assessment and sensitivity analyses were run to forecast the population trends of a seemingly robust but isolated swamp wallaby (Wallabia bicolor) population living in peri-urban Sydney, Australia; a population exposed to anthropogenic disturbances from towns, hobby farms and roads. Modeling suggested this population was in a slow decline and that predictions were highly dependent upon stochastic events and the precision of reproduction rates. However, a number of management options are identified that will dramatically reduce the risk of total population decline, with complementary options utilized in tandem the most effective.     

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.