title: Estimating replicability of classifier learning experiments

authors: Bouckaert, Remco R.

subjects: computer science

abstract: Replicability of machine learning experiments measures how likely it is that the outcome of one experiment is repeated when performed with a different randomization of the data. In this paper, we present an estimator of replicability of an experiment that is efficient. More precisely, the estimator is unbiased and has lowest variance in the class of estimators formed by a linear combination of outcomes of experiments on a given data set. We gathered empirical data for comparing experiments consisting of different sampling schemes and hypothesis tests. Both factors are shown to have an impact on replicability of experiments. The data suggests that sign tests should not be used due to low replicability. Ranked sum tests show better performance, but the combination of a sorted runs sampling scheme with a t-test gives the most desirable performance judged on Type I and II error and replicability.

text: Estimating replicability of classifier learning experiments Replicability of machine learning experiments measures how likely it is that the outcome of one experiment is repeated when performed with a different randomization of the data. In this paper, we present an estimator of replicability of an experiment that is efficient. More precisely, the estimator is unbiased and has lowest variance in the class of estimators formed by a linear combination of outcomes of experiments on a given data set. We gathered empirical data for comparing experiments consisting of different sampling schemes and hypothesis tests. Both factors are shown to have an impact on replicability of experiments. The data suggests that sign tests should not be used due to low replicability. Ranked sum tests show better performance, but the combination of a sorted runs sampling scheme with a t-test gives the most desirable performance judged on Type I and II error and replicability.

year: 2004

title: Tephrochronology and its application: A review

authors: Lowe, David J.

subjects: tephras

abstract: Tephrochronology (from tephra, Gk ‘ashes’) is a unique stratigraphic method for linking, dating, and synchronizing geological, palaeoenvironmental, or archaeological sequences or events. As well as utilising the Law of Superposition, tephrochronology in practise requires tephra deposits to be characterized (or ‘fingerprinted’) using physical properties evident in the field together with those obtained from laboratory analyses. Such analyses include mineralogical examination (petrography) or geochemical analysis of glass shards or crystals using an electron microprobe or other analytical tools including laser-ablation-based mass spectrometry or the ion microprobe. The palaeoenvironmental or archaeological context in which a tephra occurs may also be useful for correlational purposes. Tephrochronology provides greatest utility when a numerical age obtained for a tephra or cryptotephra is transferrable from one site to another using stratigraphy and by comparing and matching inherent compositional features of the deposits with a high degree of likelihood. Used this way, tephrochronology is an age-equivalent dating method that provides an exceptionally precise volcanic-event stratigraphy. Such age transfers are valid because the primary tephra deposits from an eruption essentially have the same short-lived age everywhere they occur, forming isochrons very soon after the eruption (normally within a year). As well as providing isochrons for palaeoenvironmental and archaeological reconstructions, tephras through their geochemical analysis allow insight into volcanic and magmatic processes, and provide a comprehensive record of explosive volcanism and recurrence rates in the Quaternary (or earlier) that can be used to establish time-space relationships of relevance to volcanic hazard analysis.
The basis and application of tephrochronology as a central stratigraphic and geochronological tool for Quaternary studies are presented and discussed in this review. Topics covered include principles of tephrochronology, defining isochrons, tephra nomenclature, mapping and correlating tephras from proximal to distal locations at metre- through to sub-millimetre-scale, cryptotephras, mineralogical and geochemical fingerprinting methods, numerical and statistical correlation techniques, and developments and applications in dating including the use of flexible depositional age-modelling techniques based on Bayesian statistics. Along with reference to wide-ranging examples and the identification of important recent advances in tephrochronology, such as the development of new geoanalytical approaches that enable individual small glass shards to be analysed near-routinely for major, trace, and rare-earth elements, potential problems such as miscorrelation, erroneous-age transfer, and tephra reworking and taphonomy (especially relating to cryptotephras) are also examined. Some of the challenges for future tephrochronological studies include refining geochemical analytical methods further, improving understanding of cryptotephra distribution and preservation patterns, improving age modelling including via new or enhanced radiometric or incremental techniques and Bayesian-derived models, evaluating and quantifying uncertainty in tephrochronology to a greater degree than at present, constructing comprehensive regional databases, and integrating tephrochronology with spatially referenced environmental and archaeometric data into 3-D reconstructions using GIS and geostatistics.

text: Tephrochronology and its application: A review Tephrochronology (from tephra, Gk ‘ashes’) is a unique stratigraphic method for linking, dating, and synchronizing geological, palaeoenvironmental, or archaeological sequences or events. As well as utilising the Law of Superposition, tephrochronology in practise requires tephra deposits to be characterized (or ‘fingerprinted’) using physical properties evident in the field together with those obtained from laboratory analyses. Such analyses include mineralogical examination (petrography) or geochemical analysis of glass shards or crystals using an electron microprobe or other analytical tools including laser-ablation-based mass spectrometry or the ion microprobe. The palaeoenvironmental or archaeological context in which a tephra occurs may also be useful for correlational purposes. Tephrochronology provides greatest utility when a numerical age obtained for a tephra or cryptotephra is transferrable from one site to another using stratigraphy and by comparing and matching inherent compositional features of the deposits with a high degree of likelihood. Used this way, tephrochronology is an age-equivalent dating method that provides an exceptionally precise volcanic-event stratigraphy. Such age transfers are valid because the primary tephra deposits from an eruption essentially have the same short-lived age everywhere they occur, forming isochrons very soon after the eruption (normally within a year). As well as providing isochrons for palaeoenvironmental and archaeological reconstructions, tephras through their geochemical analysis allow insight into volcanic and magmatic processes, and provide a comprehensive record of explosive volcanism and recurrence rates in the Quaternary (or earlier) that can be used to establish time-space relationships of relevance to volcanic hazard analysis.
The basis and application of tephrochronology as a central stratigraphic and geochronological tool for Quaternary studies are presented and discussed in this review. Topics covered include principles of tephrochronology, defining isochrons, tephra nomenclature, mapping and correlating tephras from proximal to distal locations at metre- through to sub-millimetre-scale, cryptotephras, mineralogical and geochemical fingerprinting methods, numerical and statistical correlation techniques, and developments and applications in dating including the use of flexible depositional age-modelling techniques based on Bayesian statistics. Along with reference to wide-ranging examples and the identification of important recent advances in tephrochronology, such as the development of new geoanalytical approaches that enable individual small glass shards to be analysed near-routinely for major, trace, and rare-earth elements, potential problems such as miscorrelation, erroneous-age transfer, and tephra reworking and taphonomy (especially relating to cryptotephras) are also examined. Some of the challenges for future tephrochronological studies include refining geochemical analytical methods further, improving understanding of cryptotephra distribution and preservation patterns, improving age modelling including via new or enhanced radiometric or incremental techniques and Bayesian-derived models, evaluating and quantifying uncertainty in tephrochronology to a greater degree than at present, constructing comprehensive regional databases, and integrating tephrochronology with spatially referenced environmental and archaeometric data into 3-D reconstructions using GIS and geostatistics.

year: 2011

title: Local Cryo-history: Redefining the creation, transformation and circulation of Aotearoa’s nineteenth century glacier knowledge

authors: Annandale, Claudi - Ann

abstract: The creation, transformation and dissemination of knowledge constantly shapes the narrative of glacier history. However, the intersecting layers that human encounters with the frozen environment, Indigenous knowledge, and popular thought add to glacier histories is often overlooked. By analysing the trends and intellectual traditions that emerged in nineteenth century New Zealand, a period defined as glaciology's 'classical' era of study, this thesis aims to broaden the Southern Alps’ local science-focused glacier discourse.   

Māori, for example, possessed unique mātauranga (knowledge) that was documented through Europeans employing local guides to accompany them across the Southern Alps. This mātauranga shaped some encounters nineteenth-century scientists, surveyors, and travellers had with Kā Tiritiri o te Moana’s glacier environment. New Zealand scholars like Julius von Haast and James Hector, on the other hand, further refined their understanding of New Zealand glaciers through the transnational exchange of knowledge and intellectual debates. A combination of Enlightenment rationalism and Romantic aesthetic also influenced popular glacier narratives that emerged during the nineteenth century. For example, the imagination of journalists, mountaineers and travellers reflected the broader cultural trends that circulated from Europe to New Zealand before their knowledge was disseminated to the public.  

By interrogating mātauranga Māori, formal scientific study, and popular settler imagination about glaciers, this thesis redefines New Zealand’s nineteenth-century glacier history as inherently multilayered through the circulation, creation, transformation and dissemination of glacier knowledge. In doing so, it highlights glaciers not only as physical entities defined by scientific study but as ideas shaped by diverse knowledge systems, cultural perceptions, and historical contingencies.

text: Local Cryo-history: Redefining the creation, transformation and circulation of Aotearoa’s nineteenth century glacier knowledge The creation, transformation and dissemination of knowledge constantly shapes the narrative of glacier history. However, the intersecting layers that human encounters with the frozen environment, Indigenous knowledge, and popular thought add to glacier histories is often overlooked. By analysing the trends and intellectual traditions that emerged in nineteenth century New Zealand, a period defined as glaciology's 'classical' era of study, this thesis aims to broaden the Southern Alps’ local science-focused glacier discourse.   

Māori, for example, possessed unique mātauranga (knowledge) that was documented through Europeans employing local guides to accompany them across the Southern Alps. This mātauranga shaped some encounters nineteenth-century scientists, surveyors, and travellers had with Kā Tiritiri o te Moana’s glacier environment. New Zealand scholars like Julius von Haast and James Hector, on the other hand, further refined their understanding of New Zealand glaciers through the transnational exchange of knowledge and intellectual debates. A combination of Enlightenment rationalism and Romantic aesthetic also influenced popular glacier narratives that emerged during the nineteenth century. For example, the imagination of journalists, mountaineers and travellers reflected the broader cultural trends that circulated from Europe to New Zealand before their knowledge was disseminated to the public.  

By interrogating mātauranga Māori, formal scientific study, and popular settler imagination about glaciers, this thesis redefines New Zealand’s nineteenth-century glacier history as inherently multilayered through the circulation, creation, transformation and dissemination of glacier knowledge. In doing so, it highlights glaciers not only as physical entities defined by scientific study but as ideas shaped by diverse knowledge systems, cultural perceptions, and historical contingencies.

year: 2025