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- Häggström, Jenny, 1980-
(författare)
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Selection of smoothing parameters with application in causal inference
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is a contribution to the research area concerned with selection of smoothing parameters in the framework of nonparametric and semiparametric regression. Selection of smoothing parameters is one of the most important issues in this framework and the choice can heavily influence subsequent results. A nonparametric or semiparametric approach is often desirable when large datasets are available since this allow us to make fewer and weaker assumptions as opposed to what is needed in a parametric approach. In the first paper we consider smoothing parameter selection in nonparametric regression when the purpose is to accurately predict future or unobserved data. We study the use of accumulated prediction errors and make comparisons to leave-one-out cross-validation which is widely used by practitioners. In the second paper a general semiparametric additive model is considered and the focus is on selection of smoothing parameters when optimal estimation of some specific parameter is of interest. We introduce a double smoothing estimator of a mean squared error and propose to select smoothing parameters by minimizing this estimator. Our approach is compared with existing methods.The third paper is concerned with the selection of smoothing parameters optimal for estimating average treatment effects defined within the potential outcome framework. For this estimation problem we propose double smoothing methods similar to the method proposed in the second paper. Theoretical properties of the proposed methods are derived and comparisons with existing methods are made by simulations.In the last paper we apply our results from the third paper by using a double smoothing method for selecting smoothing parameters when estimating average treatment effects on the treated. We estimate the effect on BMI of divorcing in middle age. Rich data on socioeconomic conditions, health and lifestyle from Swedish longitudinal registers is used.
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| 2. |
- Nambiar, Sanjay, 1997-
(författare)
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Adaptive Automation for Customized Products
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In today’s fast-paced industrial landscape, the drive for greater efficiency and flexibility in product development has sparked significant interest in innovative automation technologies. This thesis explores the usefulness of various automation techniques for customized products such as Knowledge-Based Engineering (KBE), Multidisciplinary Optimization (MDO) and machine learning frameworks.The research begins by establishing an automated framework for fixture design, combining design automation and MDO to streamline the design process. It then moves to optimizing gas turbines, introducing an automation framework that merges CAD templates with KBE principles.For complex and unstructured production, this thesis explores the use of Reinforcement Learning (RL) to tackle challenges in unstructured manufacturing. By utilizing lightweight physics-based engines and RL, the research advances automated assembly validation and mobile robot operations, pushing the boundaries of adaptive production automation. Furthermore, a framework is developed, which integrates smoothly with industrial robotic platforms showcases practical automation solutions and highlights the adaptability and applicability of digital twin technology in real-world situations.This thesis contributes to the field of product development by providing innovative solutions that are rooted in multidisciplinary research. It bridges the theoretical and practical aspects of automation with solutions that overcomes the obstacles to realize seamless integration between digital and physical realities in a manufacturing context.
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| 3. |
- Wallin, Gabriel, 1991-
(författare)
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Extensions of the kernel method of test score equating
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis makes contributions within the area of test score equating and specifically kernel equating. The first paper of this thesis studies the estimation of the test score distributions needed in kernel equating. There are currently two families of models implemented within kernel equating for this purpose, namely log-linear models and item response theory models. The impact of model selection criteria for these models on the equated scores are studied using both empirical and simulated data.The second paper focuses on the continuization of the estimated score distributions, where different bandwidth selection methods are studied. The study considers multiple data collection designs, sample sizes and score distributions and investigates how large impact the bandwidth selection has on the equated scores.When the test groups differ in their ability distributions it is necessary to adjust for such differences to make fair comparisons possible. The most common way of adjusting for ability imbalance is by using items that are common for both test forms, known as anchor items. If no such items are available, it has been suggested to use background information about the test-takers instead. However, when the covariate vector of background information increases, the combination of covariates with no observations tends to increase as well. The third paper of this thesis therefore suggests to transform the covariate vector into a scalar propensity score. Two equating estimators are suggested under this setting and the standard error of equating (SEE) for both estimators are given.The SEE for kernel equating has previously been derived using the delta method. The fourth paper revisits the Bahadur representation of sample quantiles to derive the SEE. Both methods of calculating the SEE are compared, and it is shown that they are equivalent for all common data collection designs when the terms of the Bahadur SEE are estimated using Taylor expansions. An implementation of an alternative estimator of the Bahadur SEE for which the equivalence result does not hold is also included to illustrate when the two methods differ.
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