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The research activities within each of AUT’s five faculties are overseen by an Associate Dean of Research who works closely with the Pro Vice-Chancellor Research, Innovation and Enterprise. We encourage you to explore the broad suite of research activities from each faculties. Full text digital files are available open access for all items.

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Browsing AUT Faculties by Subject "0104 Statistics"

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    A Mixture Distribution for Modelling Bivariate Ordinal Data
    (Springer, 2024-05-20) Ip, Ryan HL; Wu, KYK
    Ordinal responses often arise from surveys which require respondents to rate items on a Likert scale. Since most surveys contain more than one question, the data collected are multivariate in nature, and the associations between different survey items are usually of considerable interest. In this paper, we focus on a mixture distribution, called the combination of uniform and binomial (CUB), under which each response is assumed to originate from either the respondent’s uncertainty or the actual feeling towards the survey item. We extend the CUB model to the bivariate case for modelling two correlated ordinal data without using copula-based approaches. The proposed model allows the associations between the unobserved uncertainty and feeling components of the variables to be estimated, a distinctive feature compared to previous attempts. This article describes the underlying logic and deals with both theoretical and practical aspects of the proposed model. In particular, we will show that the model is identifiable under a wide range of conditions. Practical inferential aspects such as parameter estimation, standard error calculations and hypothesis tests will be discussed through simulations and a real case study.
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    Vertical Distribution of Airborne Microorganisms Over Forest Environments: A Potential Source of Ice-Nucleating Bioaerosols
    (Elsevier BV, 2023-03-28) Maki, Teruya; Hosaka, Kentaro; Lee, Kevin C; Kawabata, Yasuhiro; Kajino, Mizuo; Uto, Maoto; Kita, Kazuyuki; Igarashi, Yasuhito
    Airborne microorganisms transported from forested areas can influence cloud formation by forming ice nuclei. However, the vertical transportation of airborne microorganisms over forested areas is not well understood. We collected aerosols at three heights, [ground (2 m), canopy top (20 m), and above canopy (500 m)] during the summer, fall and winter, to analyze the airborne microbial communities that were distributed vertically over the forest. During summer and fall, the microbial particles maintained similar concentrations in the forest zone (canopy top and ground) and decreased to 1/10th of the microbial concentration in the above canopy area. The particle concentrations in winter indicated efficient vertical mixing below 500 m. High-throughput DNA sequencing revealed that the airborne microbial communities were composed of terrestrial and phyllospheric species associated with the degradation of decaying plant litters. Regardless of the three seasons, the above canopy was dominated by atmospheric stress-resistant bacteria from the phyla Actinobacteria and Firmicutes. Unlike bacteria, the mushroom-type fungal members of Agaricomycetes grew in relative abundance above the canopy, primarily throughout the summer and winter, while mold-type fungal Dothideomycetes species were often found at all three heights during the fall. The Fusarium, Pseudomonas, and Bacillus isolates, which were obtained from air samples at three heights, indicated high activities of ice nucleation in the water-drop freezing assay. Therefore, ice-nucleating microbial taxa likely originated from fungal and bacterial communities in the soil litter and plant surfaces of the phyllospheric environments.
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