Query Learning with Exponential Query Costs

In query learning, the goal is to identify an unknown object while minimizing the number of "yes" or "no" questions (queries) posed about that object. A well-studied algorithm for query learning is known as generalized binary search (GBS). We show that GBS is a greedy algorithm to optimize the expected number of queries needed to identify the unknown object. We also generalize GBS in two ways. First, we consider the case where the cost of querying grows exponentially in the number of queries and the goal is to minimize the expected exponential cost. Then, we consider the case where the objects are partitioned into groups, and the objective is to identify only the group to which the object belongs. We derive algorithms to address these issues in a common, information-theoretic framework. In particular, we present an exact formula for the objective function in each case involving Shannon or Renyi entropy, and develop a greedy algorithm for minimizing it. Our algorithms are demonstrated on two applications of query learning, active learning and emergency response.Comment: 15 page

Counting Chickens When They Hatch: The Short-term Effect of Aid on Growth

Past research on aid and growth is flawed because it typically examines the impact of aggregate aid on growth over a short period, usually four years, while significant portions of aid are unlikely to affect growth in such a brief time. We divide aid into three categories: (1) emergency and humanitarian aid (likely to be negatively correlated with growth); (2) aid that affects growth only over a long period of time, if at all, such as aid to support democracy, the environment, health, or education (likely to have no relationship to growth over four years); and (3) aid that plausibly could stimulate growth in four years, including budget and balance of payments support, investments in infrastructure, and aid for productive sectors such as agriculture and industry. Our focus is on the third group, which accounts for about 53% of all aid flows. We find a positive, causal relationship between this “short-impact” aid and economic growth (with diminishing returns) over a four-year period. The impact is large: at least two-to-three times larger than in studies using aggregate aid. Even at a conservatively high discount rate, at the mean a $1 increase in short-impact aid raises output (and income) by$1.64 in present value in the typical country. From a different perspective, we find that higher-than-average short-impact aid to sub- Saharan Africa raised per capita growth rates there by about half a percentage point over the growth that would have been achieved by average aid flows. The results are highly statistically significant and stand up to a demanding array of tests, including various specifications, endogeneity structures, and treatment of influential observations. The basic result does not depend crucially on a recipient’s level of income or quality of institutions and policies; we find that short-impact aid causes growth, on average, regardless of these characteristics. However, we find some evidence that the impact on growth is somewhat larger in countries with stronger institutions or longer life expectancies (better health). We also find a significant negative relationship between debt repayments and growth. We make no statement on, and do not attempt to measure, any additional effect on growth from other categories of aid (e.g., emergency assistance or aid that might affect growth over a longer time period); four-year panel regressions are not an appropriate tool to examine those relationships.foreign aid, humanitarian aid, short impact, economic growth

Between Replication and Docking: "Adaptive Agents, Political Institutions, and Civic Traditions" Revisited

This article has two primary objectives: (i) to replicate an agent-based model of social interaction by Bhavnani (2003), in which the author explicitly specifies mechanisms underpinning Robert Putnam\'s (1993) work on Civic Traditions in Modern Italy, bridging the gap between the study\'s historical starting point—political regimes that characterized 14th Century Italy—and contemporary levels of social capital—reflected in a \'civic\' North and an \'un-civic\' South; and (ii) to extend the original analysis, using a landscape of Italy that accounts for population density. The replication exercise is performed by different authors using an entirely distinct ABM toolkit (PS-I) with its own rule set governing agent-interaction and cultural change. The extension, which more closely approximates a docking exercise, utilizes equal area cartograms otherwise known as density-equalizing maps (Gastner and Newman 2004) to resize the territory according to 1993 population estimates. Our results indicate that: (i) using the criterion of distributional equivalence, we experience mixed success in replicating the original model given our inability to restrict the selection of partners to \'eligible\' neighbors and limit the number of agent interactions in a timestep; (ii) increasing the number of agents and introducing more realistic population distributions in our extension of the replication model increases distributional equivalence; (iii) using the weaker criteria of relational alignment, both the replication model and its extension capture the basic relationship between institutional effectiveness and civic change, the effect of open boundaries, historical shocks, and path dependence; and (iv) that replication and docking may be usefully combined in model-to-model analysis, with an eye towards verification, reimplementation, and alignment.Replication, Docking, Agent-Based Model, Italy, Social Capital

Towards a model of information scatter: Implications for search and design

Recent studies suggest that users often retrieve incomplete healthcare information because of the complex and skewed distribution of facts across relevant webpages. To understand the causes for such skewed distributions, this paper presents the results of two analyses: (1) A distribution analysis discusses how facts related to healthcare topics are scattered across high-quality healthcare pages. (2) A cluster analysis of the same data suggests that the skewed distribution can be explained by the existence of three page profiles that vary in information density, each of which play in important role in providing comprehensive information of a topic. The above analyses provide clues towards a model of information scatter which describes how the design decisions by individual webpage authors could collectively lead to the scatter of information as observed in the data. The analyses also suggest implications for the design of websites, search algorithms, and search interfaces to help users find comprehensive information about a topic.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57321/1/14504301225_ftp.pd

REsCape: an Agent-Based Framework for Modeling Resources, Ethnicity, and Conflict

This research note provides a general introduction to REsCape: an agent-based computational framework for studying the relationship between natural resources, ethnicity, and civil war. By permitting the user to specify: (i) different resource profiles ranging from a purely agrarian economy to one based on the artisanal or industrial extraction of alluvial or kimberlite diamonds; (ii) different patterns of ethnic domination, ethnic polarization, and varying degrees of ethnic salience; as well as (iii) specific modes of play for key agents, the framework can be used to assess the effects of key variables — whether taken in isolation or in various combinations — on the onset and duration of civil war. Our objective is to make REsCape available as an open source toolkit in the future, one that can be used, modified, and refined by students and scholars of civil war.Agent-Based Model, Ethnicity, Salience, Polarization, Domination, Civil War, Greed, Natural Resources

Counting chickens when they hatch: The short-term effect of aid on growth

Past research on aid and growth is flawed because it typically examines the impact of aggregate aid on growth over a short period, usually four years, while significant portions of aid are unlikely to affect growth in such a brief time. We divide aid into three categories: (1) emergency and humanitarian aid (likely to be negatively correlated with growth); (2) aid that affects growth only over the long term, if at all, such as aid to support democracy, the environment, health, or education (likely to have no relationship to growth over four years); and (3) aid that plausibly could stimulate growth in four years, including budget and balance of payments support, investments in infrastructure, and aid for productive sectors such as agriculture and industry. Our focus is on the third group, which accounts for about 45% of all aid flows. We find a positive, causal relationship between this 'short-impact' aid and economic growth (with diminishing returns) over a four-year period. The impact is large: at least two-to-three times larger than in studies using aggregate aid. Even at a conservatively high discount rate, at the mean a $1 increase in short-impact aid raises output (and income) by$8 in present value in the typical country. From a different perspective, we find that higher-than-average short-impact aid to sub-Saharan Africa raised per capita growth rates there by about one percentage point over the growth that would have been achieved by average aid flows. The results are highly statistically significant and stand up to a demanding array of tests, including various specifications, endogeneity structures, and treatment of influential observations. The basic result does not depend crucially on a recipient's level of income or quality of institutions and policies; we find that short-impact aid causes growth, on average, regardless of these characteristics. However, we find some evidence that the impact on growth is somewhat larger in countries with stronger institutions or longer life expectancies (better health). We also find a significant negative relationship between debt repayments and growth. We make no statement on, and do not attempt to measure, any additional long-run effects of aid; four-year panel regressions are not an appropriate tool to examine those relationships.Foreign aid, development assistance, effectiveness, impact, growth, Burnside and Dollar, institutions, timing, interaction, effect, oda, humanitarian, short-term, short-run, long-term, long-run, disaggregated, disaggregation, disaggregate, budget support, social sector, cross-country, international

Development and preliminary evaluation of a clinical guidance programme for the decision about prophylactic oophorectomy in women undergoing a hysterectomy

Objectives: To develop a decision analysis based and computerised clinical guidance programme (CGP) that provides patient specific guidance on the decision whether or not to undergo a prophylactic oophorectomy to reduce the risk of subsequent ovarian cancer and to undertake a preliminary pilot and evaluation. Subjects: Women who had already agreed to have a hysterectomy who otherwise had no ovarian pathology. Setting: Oophorectomy decision consultation at the outpatient or pre-admission clinic. Methods: A CGP was developed with advice from gynaecologists and patient groups, incorporating a set of Markov models within a decision analytical framework to evaluate the benefits of undergoing a prophylactic oophorectomy or not on the basis of quality adjusted life expectancy, life expectancy, and for varying durations of hormone replacement therapy. Sensitivity analysis and preliminary testing of the CGP were undertaken to compare its overall performance with established guidelines and practice. A small convenience sample of women invited to use the CGP were interviewed, the interviews were taped and transcribed, and a thematic analysis was undertaken. Results: The run time of the programme was 20 minutes, depending on the use of opt outs to default values. The CGP functioned well in preliminary testing. Women were able to use the programme and expressed overall satisfaction with it. Some had reservations about the computerised format and some were surprised at the specificity of the guidance given. Conclusions: A CGP can be developed for a complex healthcare decision. It can give evidence-based health guidance which can be adjusted to account for individual risk factors and reflects a patient’s own values and preferences concerning health outcomes. Future decision aids and support systems need to be developed and evaluated in a way which takes account of the variation in patients’ preferences for inclusion in the decision making process

Interferometric study of natural convection heat transfer from a vertical flat plate with transverse roughness elements

The study of natural convection heat transfer is of significance in several areas of technology. Natural convection represents a limit on the heat transfer rate and this becomes a very important consideration for situations in which other modes are either not possible or not practical. Natural convection from vertical surfaces with some sort of large-scale surface roughness elements is encountered in many technological applications. Of particular interest is the dissipation of heat from electronic circuits, where component performance and reliability are strongly dependent on operating temperature. Natural convection is an inherently reliable cooling process. Circuit boards represent a naturally enhanced free convection situation. In other applications, it may be necessary to enhance the surface to achieve the desired temperature level;The present research was undertaken to provide information on the nature of heat transfer from rough surfaces. An interferometric technique was used to experimentally measure local heat transfer coefficients. This method is essentially non-intrusive and therefore extremely suitable for the study of low-flux phenomena such as natural convection;Several different types of surfaces were studied--namely, repeated ribbed, stepped, and sinusoidal surfaces. The effects of parameters such as protuberance height-to-spacing ratios, amplitude of spacing, conductivity of ribs, leading edge geometry, and angle of inclination were studied;It was found that heat transfer enhancement was possible in laminar natural convection using transverse roughness elements with proper sizing and shape selection. The heat transfer from the ribbed surfaces was found to be less than that from a plane flat plate of equal projected area. It was found that stepped surfaces could be used to improve the heat transfer performance relative to a plane flat plate of equal projected area. The study indicated the presence of an optimum step-pitch-to-height ratio. The performance of sinusoidal surfaces was not significantly different from that of a plane flat plate of equal projected area at low amplitude-to-wavelength ratios. The heat transfer performance decreased as the amplitude-to-wavelength ratio increased. The study also showed that roughness elements induced an early transition to turbulent flow