title: A diversity-aware model for majority vote ensemble accuracy

authors: Lim, Nick Jin Sean

subjects: Science & Technology

abstract: Ensemble classifiers are a successful and popular approach for classification, and are frequently found to have better generalization performance than single models in practice. Although it is widely recognized that ‘diversity’ between ensemble members is important in achieving these performance gains, for classification ensembles it is not widely understood which diversity measures are most predictive of ensemble performance, nor how large an ensemble should be for a particular application. In this paper, we explore the predictive power of several common diversity measures and show – with extensive experiments – that contrary to earlier work that finds no clear link between these diversity measures (in isolation) and ensemble accuracy instead by using the ρ diversity measure of Sneath and Sokal as an estimator for the dispersion parameter of a Polya-Eggenberger distribution we can predict, independently of the choice of base classifier family, the accuracy of a majority vote classifier ensemble ridiculously well. We discuss our model and some implications of our findings – such as diversity-aware (non-greedy) pruning of a majority-voting ensemble.

text: A diversity-aware model for majority vote ensemble accuracy Ensemble classifiers are a successful and popular approach for classification, and are frequently found to have better generalization performance than single models in practice. Although it is widely recognized that ‘diversity’ between ensemble members is important in achieving these performance gains, for classification ensembles it is not widely understood which diversity measures are most predictive of ensemble performance, nor how large an ensemble should be for a particular application. In this paper, we explore the predictive power of several common diversity measures and show – with extensive experiments – that contrary to earlier work that finds no clear link between these diversity measures (in isolation) and ensemble accuracy instead by using the ρ diversity measure of Sneath and Sokal as an estimator for the dispersion parameter of a Polya-Eggenberger distribution we can predict, independently of the choice of base classifier family, the accuracy of a majority vote classifier ensemble ridiculously well. We discuss our model and some implications of our findings – such as diversity-aware (non-greedy) pruning of a majority-voting ensemble.

year: 2020

title: Lake restoration: Does sediment capping have post-application effects on zooplankton and phytoplankton?

authors: Özkundakci, Deniz

subjects: Eutrophication

abstract: Although in situ sediment capping is frequently used to reduce internal loading of contaminants and nutrients, post-application assessment rarely includes the potential undesirable short-term effects on plankton species composition. We hypothesised  that a modified zeolite (Z2G1) application as a sediment capping agent in Lake Okaro, New Zealand, could cause significant undesirable shifts in species composition of both zooplankton and phytoplankton due to burial of resting stages or interference with feeding for the zooplankton. Alternatively, we predicted that the capping agent might have no effect due to, for example, the coarse grain size of the material (1–3 mm). We used multidimensional scaling (MDS) and analysis of similarity (ANOSIM) to identify any adverse effects of Z2G1 on zooplankton and phytoplankton species composition (i.e. shifts in community structure, including species loss) by comparing the community structure before and after the Z2G1 application. We found no significant differences in species composition before and after the Z2G1 application at the depths investigated (surface and 9 m). However, all of the analyses showed statistically significant differences among seasons, indicating seasonal variations in plankton composition far outweigh those that may have resulted from the Z2G1 application. Coarse particle size, low dose rate and a restricted area where the sediment capping agent was applied were considered to be the factors limiting potential adverse effects on plankton species. Considerations of finer-grained material to increase coverage and efficacy of phosphorus adsorption require assessment for their effects on zooplankton, however, and a direct mode of application into the hypolimnion is recommended to minimise effects on zooplankton and phytoplankton communities.

text: Lake restoration: Does sediment capping have post-application effects on zooplankton and phytoplankton? Although in situ sediment capping is frequently used to reduce internal loading of contaminants and nutrients, post-application assessment rarely includes the potential undesirable short-term effects on plankton species composition. We hypothesised  that a modified zeolite (Z2G1) application as a sediment capping agent in Lake Okaro, New Zealand, could cause significant undesirable shifts in species composition of both zooplankton and phytoplankton due to burial of resting stages or interference with feeding for the zooplankton. Alternatively, we predicted that the capping agent might have no effect due to, for example, the coarse grain size of the material (1–3 mm). We used multidimensional scaling (MDS) and analysis of similarity (ANOSIM) to identify any adverse effects of Z2G1 on zooplankton and phytoplankton species composition (i.e. shifts in community structure, including species loss) by comparing the community structure before and after the Z2G1 application. We found no significant differences in species composition before and after the Z2G1 application at the depths investigated (surface and 9 m). However, all of the analyses showed statistically significant differences among seasons, indicating seasonal variations in plankton composition far outweigh those that may have resulted from the Z2G1 application. Coarse particle size, low dose rate and a restricted area where the sediment capping agent was applied were considered to be the factors limiting potential adverse effects on plankton species. Considerations of finer-grained material to increase coverage and efficacy of phosphorus adsorption require assessment for their effects on zooplankton, however, and a direct mode of application into the hypolimnion is recommended to minimise effects on zooplankton and phytoplankton communities.

year: 2011

title: Population diversity in Aotearoa New Zealand: Insights from the CaDDANZ research programme

authors: Stone, Geoff

abstract: CaDDANZ was a New Zealand Government-funded project studying the impacts of growing population diversity in Aotearoa New Zealand. The project ran from 2014 to 2020 and was extended to March 2021 due to the effects of the global COVID-19 pandemic. Staffed by a multidisciplinary team of researchers, CaDDANZ aimed to identify changing demographics and the impacts of ethnic and demographic diversity on aspects of economic and social change. This report has synthesised a bundle of key insights that could only have surfaced through the reflection on the interplay between the research questions that the original bid set out to address. While we, as a project team, did not intend to produce transdisciplinary or even interdisciplinary work on migration, diversity or the diversity dividend, setting a goal to synthesise something from the project as a whole has produced this report. Using social cohesion as a sorting mechanism for the insights has meant this overview is selective and high level. Not all the projects can be read against a social cohesion or even social inclusion lens. In particular, many of the econometric outputs explicitly addressed aspects of diversity as an economic dividend and that work is not highlighted in the synthesis. 
Three broad themes are addressed 
1. Immigration and diversity – understanding population trends 
2. [Re] conceptualising ethno-demographic diversity in Aotearoa – Tangata whenua perspectives 
3. Diversity in context – in different settings and over time 
The report concludes with four high-level insights 
1. Immigration policy needs to re-examine its position in relation to Tiriti o Waitangi where any Crown partnership relationship is currently lacking. 
2. Despite social cohesion being a negotiated term, its use as a framing for the impacts of migration on both the host country and individual migrant lives is underpinned by its use in the Royal Commission of Inquiry into the terrorist attack on Christchurch mosques on 15 March 2019 and is preferable to the concept of a diversity dividend.1 
3. While ethnocultural diversity is the default for ‘diversity dividend’ research, the concept of the social organisation of difference has broader relevance to social justice-oriented policy development.2 
4. The use of wide range of different methodologies is vital for the production of wellevidenced, theory-informed strategies and policies.

text: Population diversity in Aotearoa New Zealand: Insights from the CaDDANZ research programme CaDDANZ was a New Zealand Government-funded project studying the impacts of growing population diversity in Aotearoa New Zealand. The project ran from 2014 to 2020 and was extended to March 2021 due to the effects of the global COVID-19 pandemic. Staffed by a multidisciplinary team of researchers, CaDDANZ aimed to identify changing demographics and the impacts of ethnic and demographic diversity on aspects of economic and social change. This report has synthesised a bundle of key insights that could only have surfaced through the reflection on the interplay between the research questions that the original bid set out to address. While we, as a project team, did not intend to produce transdisciplinary or even interdisciplinary work on migration, diversity or the diversity dividend, setting a goal to synthesise something from the project as a whole has produced this report. Using social cohesion as a sorting mechanism for the insights has meant this overview is selective and high level. Not all the projects can be read against a social cohesion or even social inclusion lens. In particular, many of the econometric outputs explicitly addressed aspects of diversity as an economic dividend and that work is not highlighted in the synthesis. 
Three broad themes are addressed 
1. Immigration and diversity – understanding population trends 
2. [Re] conceptualising ethno-demographic diversity in Aotearoa – Tangata whenua perspectives 
3. Diversity in context – in different settings and over time 
The report concludes with four high-level insights 
1. Immigration policy needs to re-examine its position in relation to Tiriti o Waitangi where any Crown partnership relationship is currently lacking. 
2. Despite social cohesion being a negotiated term, its use as a framing for the impacts of migration on both the host country and individual migrant lives is underpinned by its use in the Royal Commission of Inquiry into the terrorist attack on Christchurch mosques on 15 March 2019 and is preferable to the concept of a diversity dividend.1 
3. While ethnocultural diversity is the default for ‘diversity dividend’ research, the concept of the social organisation of difference has broader relevance to social justice-oriented policy development.2 
4. The use of wide range of different methodologies is vital for the production of wellevidenced, theory-informed strategies and policies.

year: 2021