title: Ensembles of nested dichotomies for multi-class problems

authors: Frank, Eibe

abstract: Nested dichotomies are a standard statistical technique for tackling certain polytomous classification problems with logistic regression. They can be represented as binary trees that recursively split a multi-class classification task into a system of dichotomies and provide a statistically sound way of applying two-class learning algorithms to multi-class problems (assuming these algorithms generate class probability estimates). However, there are usually many candidate trees for a given problem and in the standard approach the choice of a particular tree is based on domain knowledge that may not be available in practice. An alternative is to treat every system of nested dichotomies as equally likely and to form an ensemble classifier based on this assumption. We show that this approach produces more accurate classifications than applying C4.5 and logistic regression directly to multi-class problems. Our results also show that ensembles of nested dichotomies produce more accurate classifiers than pairwise classification if both techniques are used with C4.5, and comparable results for logistic regression. Compared to error-correcting output codes, they are preferable if logistic regression is used, and comparable in the case of C4.5. An additional benefit is that they generate class probability estimates. Consequently they appear to be a good general-purpose method for applying binary classifiers to multi-class problems.

text: Ensembles of nested dichotomies for multi-class problems Nested dichotomies are a standard statistical technique for tackling certain polytomous classification problems with logistic regression. They can be represented as binary trees that recursively split a multi-class classification task into a system of dichotomies and provide a statistically sound way of applying two-class learning algorithms to multi-class problems (assuming these algorithms generate class probability estimates). However, there are usually many candidate trees for a given problem and in the standard approach the choice of a particular tree is based on domain knowledge that may not be available in practice. An alternative is to treat every system of nested dichotomies as equally likely and to form an ensemble classifier based on this assumption. We show that this approach produces more accurate classifications than applying C4.5 and logistic regression directly to multi-class problems. Our results also show that ensembles of nested dichotomies produce more accurate classifiers than pairwise classification if both techniques are used with C4.5, and comparable results for logistic regression. Compared to error-correcting output codes, they are preferable if logistic regression is used, and comparable in the case of C4.5. An additional benefit is that they generate class probability estimates. Consequently they appear to be a good general-purpose method for applying binary classifiers to multi-class problems.

year: 2004-07-04

title: Detection of thin tephra deposits in peat and organic lake sediments by rapid X-radiography and X-ray fluorescence techniques

authors: Lowe, David J.

abstract: This paper reports the application of the X-ray image process of X-radiography to unopened, small diameter organic sediment cores containing thin tephra deposits. Second, a rapid technique for detecting tephra layers in peat samples by X-ray fluorescence (XRF) analysis is described.

text: Detection of thin tephra deposits in peat and organic lake sediments by rapid X-radiography and X-ray fluorescence techniques This paper reports the application of the X-ray image process of X-radiography to unopened, small diameter organic sediment cores containing thin tephra deposits. Second, a rapid technique for detecting tephra layers in peat samples by X-ray fluorescence (XRF) analysis is described.

year: 1981

title: Death and homelessness on the streets of Aotearoa New Zealand: Sustaining life

authors: Charvin-Fabre, Sandrine

abstract: In high-income countries, homeless people die 20 to 35 years earlier than domiciled populations. Despite this enduring reality, the issue of death inequality remains underexplored, especially in indigenous homeless contexts, facing the ongoing effects of colonisation. This study centres on the perspectives and aspirations of a Māori street homeless community, known as the “Peeps”. Its objective is twofold: to spotlight to unjust, untimely, and avoidable mortality impacting homeless communities in Aotearoa New Zealand, and to understand how life can be sustained against the adversity of street life. The thesis diverges from conventional public health approaches, which often dichotomise early deaths prevention through improved healthcare access during homelessness, and palliative care provision at the end of life of homeless people. This thesis explores “the temporal space of life prior to death”. Within that temporal realm, the omnipresent “risk of dying” that infiltrates the lives of homeless people, disrupting the linear progression toward death observed in domiciled populations, is recognised. This temporal space is understood as a zone of uncertainty and potentiality, wherein complex life-death dynamics operate, revealing broader political, societal and cultural tensions. This study encountered significant challenges, including the dearth of prior death-related research in Māori homeless contexts, and my non-Māori identity. In response, an indeterminate approach, rooted in relational ethics and complexity and systems thinking — aligned with Māori worldviews — was adopted.  

Part I of the thesis is conceptual and contextual. Part II invites the readers into the fragile “temporal space of life prior to death” and the cyclical research process. Cycle 1 focuses on understanding the local context of death inequality, through relational fieldwork and statistical analysis of coroners’ reports. This analysis uncovers a 30-year life expectancy disparity with domiciled populations, exacerbated by three-quarters of avoidable mortality, mainly due to chronic conditions and suicide. Subsequent cycles sustain relational fieldwork, using collaborative and critical performance ethnography. Cycle 2 reveals the Peeps’ resistance to access healthcare, rooted in experiences of transgenerational trauma and marginalisation of Māori beliefs and values in relation to death and dying within mainstream healthcare institutions. Collaboration with the Peeps leads to the co-creation of a drama, intended to initiate conversations with health professionals from the Peeps’ perspectives and aspirations, to improve the quality of care. This cycle also highlights the impact of disconnection processes with whānau (family, extended family) experienced by the Peeps. Progressing further, cycle 3 illuminates healing processes with whānau using Advance Care Planning, envisioned as a relational space, providing the Peeps with a sense of belonging, and spiritual continuity in the perspective of death and dying. 
 
In addition to shedding light on the profound death inequality that affect Māori homeless people, this thesis argues for homelessness to be recognised as “complex life-threatening conditions associated with serious-related health suffering”. Accordingly, the thesis advocates the shift toward comprehensive care, inclusive of a concurrent prevention and palliation approach over the course of homelessness, to mitigate its impact on the lives of Māori homeless people and enhance holistic wellbeing.

text: Death and homelessness on the streets of Aotearoa New Zealand: Sustaining life In high-income countries, homeless people die 20 to 35 years earlier than domiciled populations. Despite this enduring reality, the issue of death inequality remains underexplored, especially in indigenous homeless contexts, facing the ongoing effects of colonisation. This study centres on the perspectives and aspirations of a Māori street homeless community, known as the “Peeps”. Its objective is twofold: to spotlight to unjust, untimely, and avoidable mortality impacting homeless communities in Aotearoa New Zealand, and to understand how life can be sustained against the adversity of street life. The thesis diverges from conventional public health approaches, which often dichotomise early deaths prevention through improved healthcare access during homelessness, and palliative care provision at the end of life of homeless people. This thesis explores “the temporal space of life prior to death”. Within that temporal realm, the omnipresent “risk of dying” that infiltrates the lives of homeless people, disrupting the linear progression toward death observed in domiciled populations, is recognised. This temporal space is understood as a zone of uncertainty and potentiality, wherein complex life-death dynamics operate, revealing broader political, societal and cultural tensions. This study encountered significant challenges, including the dearth of prior death-related research in Māori homeless contexts, and my non-Māori identity. In response, an indeterminate approach, rooted in relational ethics and complexity and systems thinking — aligned with Māori worldviews — was adopted.  

Part I of the thesis is conceptual and contextual. Part II invites the readers into the fragile “temporal space of life prior to death” and the cyclical research process. Cycle 1 focuses on understanding the local context of death inequality, through relational fieldwork and statistical analysis of coroners’ reports. This analysis uncovers a 30-year life expectancy disparity with domiciled populations, exacerbated by three-quarters of avoidable mortality, mainly due to chronic conditions and suicide. Subsequent cycles sustain relational fieldwork, using collaborative and critical performance ethnography. Cycle 2 reveals the Peeps’ resistance to access healthcare, rooted in experiences of transgenerational trauma and marginalisation of Māori beliefs and values in relation to death and dying within mainstream healthcare institutions. Collaboration with the Peeps leads to the co-creation of a drama, intended to initiate conversations with health professionals from the Peeps’ perspectives and aspirations, to improve the quality of care. This cycle also highlights the impact of disconnection processes with whānau (family, extended family) experienced by the Peeps. Progressing further, cycle 3 illuminates healing processes with whānau using Advance Care Planning, envisioned as a relational space, providing the Peeps with a sense of belonging, and spiritual continuity in the perspective of death and dying. 
 
In addition to shedding light on the profound death inequality that affect Māori homeless people, this thesis argues for homelessness to be recognised as “complex life-threatening conditions associated with serious-related health suffering”. Accordingly, the thesis advocates the shift toward comprehensive care, inclusive of a concurrent prevention and palliation approach over the course of homelessness, to mitigate its impact on the lives of Māori homeless people and enhance holistic wellbeing.

year: 2024