Positive dependence in qualitative probabilistic networks

Qualitative probabilistic networks (QPNs) combine the conditional independence assumptions of Bayesian networks with the qualitative properties of positive and negative dependence. They formalise various intuitive properties of positive dependence to allow inferences over a large network of variables. However, we will demonstrate in this paper that, due to an incorrect symmetry property, many inferences obtained in non-binary QPNs are not mathematically true. We will provide examples of such incorrect inferences and briefly discuss possible resolutions.Comment: 10 pages, 3 figure

Control theoretic models of pointing

This article presents an empirical comparison of four models from manual control theory on their ability to model targeting behaviour by human users using a mouse: McRuer’s Crossover, Costello’s Surge, second-order lag (2OL), and the Bang-bang model. Such dynamic models are generative, estimating not only movement time, but also pointer position, velocity, and acceleration on a moment-to-moment basis. We describe an experimental framework for acquiring pointing actions and automatically fitting the parameters of mathematical models to the empirical data. We present the use of time-series, phase space, and Hooke plot visualisations of the experimental data, to gain insight into human pointing dynamics. We find that the identified control models can generate a range of dynamic behaviours that captures aspects of human pointing behaviour to varying degrees. Conditions with a low index of difficulty (ID) showed poorer fit because their unconstrained nature leads naturally to more behavioural variability. We report on characteristics of human surge behaviour (the initial, ballistic sub-movement) in pointing, as well as differences in a number of controller performance measures, including overshoot, settling time, peak time, and rise time. We describe trade-offs among the models. We conclude that control theory offers a promising complement to Fitts’ law based approaches in HCI, with models providing representations and predictions of human pointing dynamics, which can improve our understanding of pointing and inform design

Regional scale mapping of ecosystem services supply, demand, flow and mismatches in Southern Myanmar

Mapping ecosystem service (ES) supply, demand, and flow – and identifying supply/demand mismatches – has become a focus of ES research and has benefitted from recent advances in modelling techniques and their combination with Geographic Information Systems. But few studies have been done in data-scarce tropical forest frontiers and these were limited in terms of area, land uses, and number and types of ES. Aiming to evolve contemporary approaches, we used Bayesian networks to model and map nine ES across Myanmar’s Tanintharyi Region for local stakeholders. Results show that while there is a high supply of multiple ES at regional level, demand for ES in urban and rapidly developing agricultural areas is not fully covered. Further, we identified a clear connection between land tenure and ES outcomes for rural communities. Agricultural concessions and protected areas with restricted access for the local population were related to lower ES flows and more supply/demand mismatches than community forests or untenured land. For future research on local ES outcomes in tropical forest frontiers, we recommend combined mismatch and flow analyses under consideration of tenurial rights

Qualitative approaches to quantifying probabilistic networks

A probabilistic network consists of a graphical representation (a directed graph) of the important variables in a domain of application, and the relationships between them, together with a joint probability distribution over the variables. A probabilistic network allows for computing any probability of interest. The joint probability distribution factorises into conditional probability distributions such that for each variable represented in the graph a distribution is specified conditional on all possible combinations of the variable's parents in the graph. Even for a moderate sized probabilistic network, thousands of probabilities need to be specified. Often the only source of probabilistic information is the knowledge and experience of experts. People, even experts, are known not be very good at assessing probabilities, and often dislike expressing their estimates as numbers. To overcome this problem, we propose two qualitative approaches to quantifying probabilistic networks. The first approach is abstracting away from probabilities by using qualitative probabilistic networks. The second approach is to allow the use of verbal expressions of probability during elicitation. In qualitative probabilistic networks, the arcs of the directed graph are augmented with signs: `+',`-', `0', and `?', indicating the direction of shift in probability for the variable at one end of the arc, given a shift in values of the variable at the other end of the arc. For example, a positive influence of variable A on variable B indicates that higher values for B become more likely given higher values for A. Qualitative probabilistic networks allow for reasoning with probabilistic networks in a qualitative way, thereby enabling us to check the robustness of the network's structure before probabilities are assessed. In addition, the qualitative signs provide constraints on the probabilities to be elicited. Qualitative networks are, however, not very expressive and therefore easily result in uninformative answers (`?'s) during reasoning. We will suggest several refinements of the formalism of qualitative probabilistic networks that enhance their expressiveness and applicability. To make probability elicitation easier on experts, we allow them to state verbal probability expressions, such as "probable" and "impossible", as well as numbers. To this end, we have augmented a vertical probability elicitation scale with verbal expressions. These expressions, and their position on the scale, are the result of several studies we conducted. The scale, together with other ingredients such as text-fragments describing the probability to be assessed and grouping of the probabilities that should sum to 1, is used in a newly designed probability elicitation method. The method provides for the elicitation of initial rough assessments. Assessments for which the outcome of the network is very sensitive can be refined using additional experts and/or the more conventional elicitation methods. Our method has been used with two experts in oncology in the construction of a probabilistic network for oesophageal carcinoma and allows us to elicit a large number of probabilities in little time. The experts felt comfortable with the method and evaluations of the resulting network have shown that it performs quite well with the rough assessments

Ecosystem services for communities in forest frontiers: An assessment of nature’s benefits to local stakeholders under different land use and tenure systems in a tropical frontier landscape in Myanmar

Tropical forest frontier landscapes are subject to land use changes and different claims on land by various actors, often leading to trade-offs and a general decline in ecosystem services (ES) for local communities. However, few comprehensive ES studies have been done in such data-scarce frontier regions and they are limited in terms of area, land uses, and number and types of ES assessed. This doctoral thesis aimed to analyse how local stakeholders in Myanmar’s Tanintharyi Region can benefit from various ES and how these are associated to different factors such as land use, land tenure, market access, or population structures. Applying advanced modelling techniques, I used Bayesian networks to model the supply, demand, flow and final outcomes of nine ES: subsistence foods, commercial products, fuelwood, medicinal plants, biodiversity, climate regulation, water regulation, environmental education, and cultural identity. The models were developed in an iterative process and integrated existing spatial datasets, census data and qualitative data from focus group discussions and interviews with local communities, government representatives, researchers, civil society organizations and non-governmental institutions working on land issues in Tanintharyi. I linked the nine models to spatial data to map ES supply, demand, and flow for local stakeholders across the region. Finally, I combined these maps to identify supply/demand (mis)matches as well as accessibility that particularly affects local communities. The thesis highlights the value of mosaic landscapes and the crucial role of equitable land tenure in tropical forest frontiers for providing multiple ES and enhancing human well-being