title: Reduced-error pruning with significance tests

authors: Frank, Eibe

subjects: computer science

abstract: When building classification models, it is common practice to prune them to counter spurious effects of the training data: this often improves performance and reduces model size. “Reduced-error pruning” is a fast pruning procedure for decision trees that is known to produce small and accurate trees. Apart from the data from which the tree is grown, it uses an independent “pruning” set, and pruning decisions are based on the model’s error rate on this fresh data. Recently it has been observed that reduced-error pruning overfits the pruning data, producing unnecessarily large decision trees. This paper investigates whether standard statistical significance tests can be used to counter this phenomenon. 
The problem of overfitting to the pruning set highlights the need for significance testing. We investigate two classes of test, “parametric” and “non-parametric.” The standard chi-squared statistic can be used both in a parametric test and as the basis for a non-parametric permutation test. In both cases it is necessary to select the significance level at which pruning is applied. We show empirically that both versions of the chi-squared test perform equally well if their significance levels are adjusted appropriately. Using a collection of standard datasets, we show that significance testing improves on standard reduced error pruning if the significance level is tailored to the particular dataset at hand using cross-validation, yielding consistently smaller trees that perform at least as well and sometimes better.

text: Reduced-error pruning with significance tests When building classification models, it is common practice to prune them to counter spurious effects of the training data: this often improves performance and reduces model size. “Reduced-error pruning” is a fast pruning procedure for decision trees that is known to produce small and accurate trees. Apart from the data from which the tree is grown, it uses an independent “pruning” set, and pruning decisions are based on the model’s error rate on this fresh data. Recently it has been observed that reduced-error pruning overfits the pruning data, producing unnecessarily large decision trees. This paper investigates whether standard statistical significance tests can be used to counter this phenomenon. 
The problem of overfitting to the pruning set highlights the need for significance testing. We investigate two classes of test, “parametric” and “non-parametric.” The standard chi-squared statistic can be used both in a parametric test and as the basis for a non-parametric permutation test. In both cases it is necessary to select the significance level at which pruning is applied. We show empirically that both versions of the chi-squared test perform equally well if their significance levels are adjusted appropriately. Using a collection of standard datasets, we show that significance testing improves on standard reduced error pruning if the significance level is tailored to the particular dataset at hand using cross-validation, yielding consistently smaller trees that perform at least as well and sometimes better.

year: 1999-06

title: Counting ourselves: Findings from the 2022 Aotearoa New Zealand trans and non-binary health survey

authors: Yee, Ashe

abstract: Counting Ourselves is a comprehensive national survey of the health and wellbeing of trans and non-binary people aged 14 and older living in Aotearoa New Zealand. The survey takes place every four years.

We report findings from 2,631 trans and non-binary people who completed our second survey in 2022. This is more than double the 1,178 survey participants from our first survey in 2018 and gives us very strong data about a range of trans and non-binary people living in Aotearoa New Zealand.

The 2022 survey participants lived in all regions of Aotearoa New Zealand and ranged in age from 14 to 86. Most were either youth aged 14–24 (53%) or adults aged 25–54 (43%). Over half (56%) of participants were non-binary, with an equal mix of trans men (22%) and trans women (22%). Compared with the general population, the survey had a higher proportion of European participants (77%), a similar proportion of Māori (14%), and a lower proportion of Asian (7%) and Pasifika (2%) participants.

More than two out of five (42%) of our participants were disabled. This included people who identified as Deaf or disabled (29%) and/or who met the definition of disability used in Stats NZ’s population surveys (38%). This was higher than the Stats NZ measure of disability in the general population (10%).

Throughout the report we identify statistically significant differences between participants based on age, gender, ethnicity, location, or disability. In 2025, the Counting Ourselves team hopes to produce fact sheets, articles, and other resources looking at the key findings for Māori, Pasifika, Asian, and disabled trans and non-binary people.

In this report we use the term gender affirming healthcare to refer to any healthcare interventions that trans or non-binary people may require to affirm their gender. We also use the term unmet need to describe the percentage of all participants who wanted but had not had a type of gender affirming healthcare.

text: Counting ourselves: Findings from the 2022 Aotearoa New Zealand trans and non-binary health survey Counting Ourselves is a comprehensive national survey of the health and wellbeing of trans and non-binary people aged 14 and older living in Aotearoa New Zealand. The survey takes place every four years.

We report findings from 2,631 trans and non-binary people who completed our second survey in 2022. This is more than double the 1,178 survey participants from our first survey in 2018 and gives us very strong data about a range of trans and non-binary people living in Aotearoa New Zealand.

The 2022 survey participants lived in all regions of Aotearoa New Zealand and ranged in age from 14 to 86. Most were either youth aged 14–24 (53%) or adults aged 25–54 (43%). Over half (56%) of participants were non-binary, with an equal mix of trans men (22%) and trans women (22%). Compared with the general population, the survey had a higher proportion of European participants (77%), a similar proportion of Māori (14%), and a lower proportion of Asian (7%) and Pasifika (2%) participants.

More than two out of five (42%) of our participants were disabled. This included people who identified as Deaf or disabled (29%) and/or who met the definition of disability used in Stats NZ’s population surveys (38%). This was higher than the Stats NZ measure of disability in the general population (10%).

Throughout the report we identify statistically significant differences between participants based on age, gender, ethnicity, location, or disability. In 2025, the Counting Ourselves team hopes to produce fact sheets, articles, and other resources looking at the key findings for Māori, Pasifika, Asian, and disabled trans and non-binary people.

In this report we use the term gender affirming healthcare to refer to any healthcare interventions that trans or non-binary people may require to affirm their gender. We also use the term unmet need to describe the percentage of all participants who wanted but had not had a type of gender affirming healthcare.

year: 2025

title: An evaluation of the effectiveness of social equity strategies for Maori students in the School of Science and Technology

authors: Rua, Mohi

subjects: Maori students

abstract: In 1991 the School of Science and Technology (SOSAT) at the University of Waikato
had a very low participation rate of Maori and students from other non-dominant
ethnic groups. This situation was serious enough to concerned the then Dean of the
School and strategies were developed to change this situation. Four major strategies
are used to encourage, support and retain Maori students to successfully pursue and
complete a degree in Science. They are: the Te Putahi o te Manawa programme - a
mentoring programme; a scholarship and grant writing strategy (in particular
assistance with Tuapapa Putaiao Maori Fellowships(TPMFs) administered by FRST);
school visits; and field trips with secondary schools in the Waikato region that have a
high proportion of Maori students. The Maori & Psychology Research Unit (MPRU) was contracted by Gary Bramley of
the Equity Office of the SOSAT to conduct this evaluation. Evaluative information was gathered through administering questionnaires,
completing key informant interviews, and completing focus group interviews. In this evaluation we sought to determine the effectiveness of the social equity
strategies for Maori students in the SOSAT at the University of Waikato.

text: An evaluation of the effectiveness of social equity strategies for Maori students in the School of Science and Technology In 1991 the School of Science and Technology (SOSAT) at the University of Waikato
had a very low participation rate of Maori and students from other non-dominant
ethnic groups. This situation was serious enough to concerned the then Dean of the
School and strategies were developed to change this situation. Four major strategies
are used to encourage, support and retain Maori students to successfully pursue and
complete a degree in Science. They are: the Te Putahi o te Manawa programme - a
mentoring programme; a scholarship and grant writing strategy (in particular
assistance with Tuapapa Putaiao Maori Fellowships(TPMFs) administered by FRST);
school visits; and field trips with secondary schools in the Waikato region that have a
high proportion of Maori students. The Maori & Psychology Research Unit (MPRU) was contracted by Gary Bramley of
the Equity Office of the SOSAT to conduct this evaluation. Evaluative information was gathered through administering questionnaires,
completing key informant interviews, and completing focus group interviews. In this evaluation we sought to determine the effectiveness of the social equity
strategies for Maori students in the SOSAT at the University of Waikato.

year: 1999-11-11