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Data Mining Practical Machine Learning Tools and Techniques

The theory of affordances

A freely available dataset produced from three million Landsat satellite images reveals substantial changes in the distribution of global surface water over the past 32 years and their causes, from climate change to human actions. The distribution of surface water has been mapped globally, and local-to-regional studies have tracked changes over time. But to date, there has been no global and methodologically consistent quantification of changes in surface water over time. Jean-Francois Pekel and colleagues have analysed more than three million Landsat images to quantify month-to-month changes in surface water at a resolution of 30 metres and over a 32-year period. They find that surface waters have declined by almost 90,000 square kilometres—largely in the Middle East and Central Asia—but that surface waters equivalent to about twice that area have been created elsewhere. Drought, reservoir creation and water extraction appear to have driven most of the changes in surface water over the past decades. The location and persistence of surface water (inland and coastal) is both affected by climate and human activity1 and affects climate2,3, biological diversity4 and human wellbeing5,6. Global data sets documenting surface water location and seasonality have been produced from inventories and national descriptions7, statistical extrapolation of regional data8 and satellite imagery9,10,11,12, but measuring long-term changes at high resolution remains a challenge. Here, using three million Landsat satellite images13, we quantify changes in global surface water over the past 32 years at 30-metre resolution. We record the months and years when water was present, where occurrence changed and what form changes took in terms of seasonality and persistence. Between 1984 and 2015 permanent surface water has disappeared from an area of almost 90,000 square kilometres, roughly equivalent to that of Lake Superior, though new permanent bodies of surface water covering 184,000 square kilometres have formed elsewhere. All continental regions show a net increase in permanent water, except Oceania, which has a fractional (one per cent) net loss. Much of the increase is from reservoir filling, although climate change14 is also implicated. Loss is more geographically concentrated than gain. Over 70 per cent of global net permanent water loss occurred in the Middle East and Central Asia, linked to drought and human actions including river diversion or damming and unregulated withdrawal15,16. Losses in Australia17 and the USA18 linked to long-term droughts are also evident. This globally consistent, validated data set shows that impacts of climate change and climate oscillations on surface water occurrence can be measured and that evidence can be gathered to show how surface water is altered by human activities. We anticipate that this freely available data will improve the modelling of surface forcing, provide evidence of state and change in wetland ecotones (the transition areas between biomes), and inform water-management decision-making.

High-resolution mapping of global surface water and its long-term changes

Social scientists often estimate models from correlational data, where the independent variable has not been exogenously manipulated; they also make implicit or explicit causal claims based on these models. When can these claims be made? We answer this question by first discussing design and estimation conditions under which model estimates can be interpreted, using the randomized experiment as the gold standard. We show how endogeneity – which includes omitted variables, omitted selection, simultaneity, common-method variance, and measurement error – renders estimates causally uninterpretable. Second, we present methods that allow researchers to test causal claims in situations where randomization is not possible or when causal interpretation could be confounded; these methods include fixed-effects panel, sample selection, instrumental variable, regression discontinuity, and difference-in-differences models. Third, we take stock of the methodological rigor with which causal claims are being made in a social sciences discipline by reviewing a representative sample of 110 articles on leadership published in the previous 10 years in top-tier journals. Our key finding is that researchers fail to address at least 66% and up to 90% of design and estimation conditions that make causal claims invalid. We conclude by offering 10 suggestions on how to improve non-experimental research.

On making causal claims : A review and recommendations

Recommender systems have been researched extensively by the Technology Enhanced Learning (TEL) community during the last decade. By identifying suitable resources from a potentially overwhelming variety of choices, such systems offer a promising approach to facilitate both learning and teaching tasks. As learning is taking place in extremely diverse and rich environments, the incorporation of contextual information about the user in the recommendation process has attracted major interest. Such contextualization is researched as a paradigm for building intelligent systems that can better predict and anticipate the needs of users, and act more efficiently in response to their behavior. In this paper, we try to assess the degree to which current work in TEL recommender systems has achieved this, as well as outline areas in which further work is needed. First, we present a context framework that identifies relevant context dimensions for TEL applications. Then, we present an analysis of existing TEL recommender systems along these dimensions. Finally, based on our survey results, we outline topics on which further research is needed.

Context-Aware Recommender Systems for Learning: A Survey and Future Challenges

This paper conducts the first detailed quantitative study of the process of publication of learning objects in repositories. This process has been often discussed theoretically, but never empirically evaluated. Several question related to basic characteristics of the publication process are raised at the beginning of the paper and answered through quantitative analysis. To provide a wide view of the publication process, this paper analyzes four types of repositories: Learning Object Repositories, Learning Object Referatories, Open Courseware Initiatives, and Learning Management Systems. For comparison, Institutional Repositories are also analyzed. Three repository characteristics are measured: size, growth, and contributor base. The main findings are that the amount of learning objects is distributed among repositories according to a power law, the repositories mostly grow linearly, and the amount of learning objects published by each contributor follows heavy-tailed distributions. The paper finally discusses the implications that this findings could have in the design and operation of Learning Object Repositories.

Quantitative Analysis of Learning Object Repositories

This paper develops the concept of relevance in the context of learning object search. It proposes a set of metrics to estimate the topical, personal and situational relevance dimensions. These metrics are derived mainly from usage and contextual information. An exploratory evaluation of the metrics shows that even the simplest ones provide statistically significant improvement in the ranking order over the most common algorithmic relevance metric. Moreover, the combination of the metrics through the RankNet learning sorts the result list 50% better than the base-line ranking. The paper also presents open questions in the field of learning object relevance ranking that deserve further attention.

Relevance Ranking Metrics for Learning Objects

Owing to the recent developments in automatic metadata generation and interoperability between digital repositories, the production of metadata is now vastly surpassing manual quality control capabilities. Abandoning quality control altogether is problematic, because low-quality metadata compromise the effectiveness of services that repositories provide to their users. To address this problem, we present a set of scalable quality metrics for metadata based on the Bruce & Hillman framework for metadata quality control. We perform three experiments to evaluate our metrics: (1) the degree of correlation between the metrics and manual quality reviews, (2) the discriminatory power between metadata sets and (3) the usefulness of the metrics as low-quality filters. Through statistical analysis, we found that several metrics, especially Text Information Content, correlate well with human evaluation and that the average of all the metrics are roughly as effective as people to flag low-quality instances. The implications of this finding are discussed. Finally, we propose possible applications of the metrics to improve tools for the administration of digital repositories.

/pdf/automatic-evaluation-of-metadata-quality-in-digital-4770v63nqt.pdf

Xavier Ochoa

Papers

Context-Aware Recommender Systems for Learning: A Survey and Future Challenges

Quantitative Analysis of Learning Object Repositories

Relevance Ranking Metrics for Learning Objects

Quantitative Analysis of Learning Object Repositories

Automatic evaluation of metadata quality in digital repositories