Thesis (M.A.)--Boston University / Some rapid approximate methods of estimating the standard deviation from samples of moderate size (20 < n < 100) are presented. The emphasis is placed on solutions of problems commonly encountered in statistical quality control, especially in the electronics industry. Factors and efficiency values are given for the use of these estimators on normally distributed data. Statistical and practical engineering and administrative criteria are suggested for testing whether particular estimators are desirable in the usual industrial situation. The estimates discussed in this paper are all order statistics, i.e. statistics which are a function of only a small number of observations selected from the whole sample. These observations are selected because of the position they occupy among the other observations when all sample observations are arranged in order of magnitude. The first estimator discussed, for instance, is the range. The range of a sample is merely the numerical difference between the largest member of the sample and the smallest member of the sample. The standard deviation of the distribution from which the sample was drawn may be estimated by dividing the range by a suitable constant. The constant is a function of the sample size and of the shape of the distribution. Factors are given for sample sizes up to ten, for the normal distribution only. [TRUNCATED]

Recently, an increasing number of researchers have attempted to overcome the constraints of size and scope in individual medical studies by estimating the overall treatment effects based on a combination of studies. A commonly used method is meta-analysis which combines results from multiple studies. The population standard deviation in primary studies is an essential quantitative value which is absent sometimes, especially when the outcome has a skewed distribution. Instead, the sample size and the sample range of the whole dataset is reported. There are several methods to estimate the standard deviation of the data based on the sample range if we assume the data are normally distributed. For example: Tippett Method2, Ramirez and Cox Method3, Hozo et al Method4, Rychtar and Taylor Method5, Mantel Method6, Sokal and Rohlf Method7 as well as Chen and Tyler Method8. Only a few papers provide a solution for estimating the population standard deviation of non-normally distributed data. In this thesis, some other distributions, which are commonly used in clinical studies, will be simulated to estimate the population standard deviation by using the methods mentioned above. The performance and the robustness of those methods for different sample sizes and different distribution parameters will be presented. Also, these methods will be evaluated on real-world datasets. This article will provide guidelines describing which methods perform best with non-normally distributed data. / Thesis / Master of Science (MSc)

In recent years there has been large increase in the amount of digital mapping data of landscapes and urban environments available through satellite imaging. This digital information can be used to develop wind flow simulators over large cities or regions for various purposes such as pollutant transport control, weather forecasts, cartography and other topographical analysis. It can also be used by architects for city planning or by game programmers for virtual reality and similar applications. But this data is massive and contains a lot of redundant information such as trees, cars, bushes, etc. For many applications, it is beneficial to reduce these huge amounts of data through elimination of unwanted information and provide a good approximate model of the original dataset. The resultant dataset can then be utilized to generate surface grids suitable for CFD purposes or can be used directly for real-time rendering or other graphics applications. Digital Elevation Model, DEM, is the most basic data type in which this digital data is available. It consists of a sampled array of elevations for ground positions that are regularly spaced in a Cartesian coordinate system. The purpose of this research is to construct and test a simple and economical prototype which caters to image procesing and data reduction of DEM images through noise elimination and compact representations of complex objects in the dataset. The model is aimed at providing a synergy between resultant image quality and its size through the generation of various levels of detail. An alternate approach using the concepts of standard deviation helps in achieving the desired goal and the results obtained by testing the model on Salt Lake City dataset verify the claims. Thus, this thesis is aimed at DEM image processing to provide a simple and compact representation of complex objects encountered in large scale urban environment datasets and reduce the size of the dataset to accommodate efficient storage, computation, fast transmission across networks and interactive visualization.

This empirical study has shown that optimal portfolios need approximately 10 securities to diversify away the unsystematic risk. This challenges previous studies of randomly chosen portfolios which states that at least 30 securities are needed. The result of this study sheds light upon the difference in risk diversification between random portfolios and optimal portfolios and is a valuable contribution for investors. The study suggests that a major part of the unsystematic risk in a portfolio can be diversified away with fewer securities by using portfolio optimization. Individual investors especially, who usually have portfolios consisting of few securities, benefit from these results. There are today multiple user-friendly software applications that can perform the computations of portfolio optimization without the user having to know the mathematics behind the program. Microsoft Excel’s solver function is an example of a well-used software for portfolio optimization. In this study however, MATLAB was used to perform all the optimizations. The study was executed on data of 140 stocks on NASDAQ Stockholm during 2000-2014. Multiple optimizations were done with varying input in order to yield a result that only depended on the investigated variable, that is, how many different stocks that are needed in order to diversify away the unsystematic risk in a portfolio. / <p>Osäker på examinatorns namn, tog namnet på den person som skickade mejl om betyg.</p>

Subglottic stenosis (SGS) is a narrowing of the airway in the region of the cricoid cartilage below the vocal folds and above the tracheal rings. Individuals with SGS experience difficulty breathing at rest and during exertion both of which become increasingly difficult with the level of stenosis severity. Some individuals also experience negative voice changes. Individuals whose stenoses significantly impact breathing generally require medical procedures or surgery, either balloon dilation or cricotracheal resection (CTR). CTR has been shown to improve patients' ability to breathe, but it can also result in permanent vocal changes. Alternatively, balloon dilation results in similar breathing improvements but for a relatively short period of time. Many studies have been published on the effectiveness of CTR; however, only a few have examined the effects of CTR on vocal production. The purpose of this study is to quantify the acoustic and auditory-perceptual features of subglottic stenosis and examine possible acoustic and auditory-perceptual changes in voice production following a revised CTR aimed to minimize voice impact in a group of women. A retrospective chart review identified women with idiopathic SGS who received revised CTR at The University of Utah Voice Disorders Center between 2008 and 2014. Presurgical and postsurgical groups included patients with both pre and post recordings (n = 11) as well as patients with only pre (n = 6) or post (n = 9) recordings. Acoustic quantification of voice signal periodicity, as well as cepstral, spectral, and fundamental frequency (F0) analyses were performed. Auditory-perceptual ratings of overall quality and monotonicity were performed. Cross-sectional and pre-post surgery analyses were completed. Aggregate analyses revealed that both pre and posttreatment SGS patients demonstrated voice disorders in the mild to moderate severity range. Pre-post comparisons indicated no significant voice change after surgery. Mean fundamental frequency decreased from 215 Hz (SD = 40 Hz) to 201 Hz (SD = 65 Hz). Voice disorder severity based on the cepstral spectral index of dysphoniaTM for sustained vowels decreased (i.e., improved) from 41 (SD = 41) to 25 (SD = 21) points. Semitone standard deviation (2.2 semitones) was equivalent from pretreatment to posttreatment. Auditory-perceptual ratings demonstrated similar results. These preliminary results indicate that the revised CTR procedure is promising in minimizing adverse voice effects. Future research is needed to determine causative factors for pretreatment voice disorders, as well as to optimize treatments in this population.

The solar energy, or photovoltaic (PV) industry, driven by economic competition with traditional fossil energy sources, strives to produce solar panels of the highest conversion efficiency and best reliability at the lowest production cost. Solar cells based on crystalline silicon are currently the dominant commercial PV technology by a large margin, and they are likely to remain dominant for at least one decade. The problem of improvement mechanical stability of silicon wafers and finished solar cell is one of the most critical for entire PV industry. Mechanical defects in wafer and cells in the form of periphery or internal cracks can be initiated at various steps of the manufacturing process and becomes the trigger for the fracture. There are a limited number of characterization methods for crack detection but only a few of those are able to satisfy PV industry needs in sensitivity of the crack detection incorporated with the analysis time. The most promising are a Resonance Ultrasonic Vibrations (RUV) technique and Photoluminescence (PL) imaging. The RUV method was further developed in this thesis project for fast non-destructive crack detection in full-size silicon wafers and solar cells. The RUV methodology relies on deviations of the resonance frequency response curve measured on a wafer with peripheral or bulk millimeter-length crack when it is compared with identical non-cracked wafers. It was observed that statistical variations of the RUV parameters on a similarly processed silicon wafers/cells with the same geometry lead to false positive events reducing accuracy of the RUV method. A new statistical approach using three independent RUV crack detection criteria was developed and applied to resolve this issue. This approach was validated experimentally. Crack detection using RUV technique was applied to a set of production-grade Cz-Si wafers and finished solar cells from the Isofoton's S.A. (Spain) production line. Cracked solar cells rejected by the RUV method using the statistical approach were imaged with room temperature PL mapping and independently controlled with Scanning Acoustic Microscopy (SAM). A comparison of three independent techniques for crack detection, RUV, PL and SAM, was performed on selected samples. A high accuracy and selectivity of the RUV method to identify mm-size cracks in wafers and cells was confirmed.

The concurrent development (CD) project is defined as the concurrent development of both hardware and software that is integrated together later for a deliverable product. The CD Scheduling Problem (CDSP) is defined as most CD baseline project schedules being developed today are overly optimistic. That is, they finish late. This study researches those techniques being used today to produce CD project schedules and looks for ways to close the gap between the baseline project schedule and reality. In Chapter 1, the CDSP is introduced. In Chapter 2, a review is made of published works. A review is also made of commercial scheduling software applications to uncover their techniques as well as a review of organizations doing research on improving project scheduling. In Chapter 3, the components of the CDSP are analyzed for ways to improve. In Chapter 4, the overall methodology of the research is discussed to include the development of the Concurrent Development Scheduling Model (CDSM) that quantifies the factors driving optimism. The CDSM is applied to typical CD schedules with the results compared to Monte Carlo simulations of the same schedules. The results from using the CDSM on completed CD projects are also presented. The CDSM does well in predicting the outcome. In Chapter 5, the results of the experiments run to develop the CDSM are given. In Chapter 6 findings and recommendations are given. Specifically, a list of findings is given that a decision maker can use to analyze a baseline project schedule and assess the schedules optimism. These findings will help define the risks in the CD schedule. Also included is a list of actions that the decision maker may be able to take to reduce of the risk of the project to improve the chances of coming in on time.

<p>During the last decades major changes has occurred at the financial markets, meaning an increasing supply and a greater variation of financial instruments. The saving habits of the Swedish people have gone from traditional bank deposits to investments in equities, funds and bonds. All this together with the great rise in the stock market at the late 90’s has brought words like risk and return up-to-date, and is the background to the development of a new law concerning financial advising which come into force the 1th of July 2004. </p><p>The contents of the thesis can be described as three bricks, representing the survey questions. The thesis starts with descriptions of which risk- and return concepts that exists and which are used by the contemporary financial institutions. Further on, the thesis deals with the individuals’ perception of risk, in particular financial risk. To end with, details regarding how a message should be conveyed are given. The three bricks together fulfil the purpose of the thesis; To investigate how the meaning of financial risk in a simple and pedagogical way can be explained to a person not familiar with financial literature, and to develop questions that facilitate when an individuals risk profile is ascertained. </p><p>We have found that standard deviation is the risk concept that dominates in financial theory, and together with Value at Risk is the most common used in practise. Good knowledge about risk is required when explaining risk. It is important to describe the information in an attractive way and use examples and illustrations. For financial advisers it also is important to have knowledge about the human behaviour, because ascertain the clients risk profile is an important part of the risk explanation. A clients risk profile is best ascertain with so called open questions where both what the clients answer and how he or she answer can form the basis for the judgement.</p>

<p>In the human body, turbulent flow is associated with many complications. Turbulence typically occurs downstream from stenoses and heart valve prostheses and at branch points of arteries. A proper way to study turbulence may enhance the understanding of the effects of stenoses and improve the functional assessment of damaged heart valves and heart valve prostheses.</p><p>The methods of today for studying turbulence in the human body lack in either precision or speed. This thesis exploits a magnetic resonance imaging (MRI) phenomenon referred to as signal loss in order to develop a method for estimating turbulence intensity in blood flow.</p><p>MRI measurements were carried out on an appropriate flow phantom. The turbulence intensity results obtained by means of the proposed method were compared with previously known turbulence intensity results. The comparison indicates that the proposed method has great potential for estimation of turbulence intensity.</p>

During the last decades major changes has occurred at the financial markets, meaning an increasing supply and a greater variation of financial instruments. The saving habits of the Swedish people have gone from traditional bank deposits to investments in equities, funds and bonds. All this together with the great rise in the stock market at the late 90’s has brought words like risk and return up-to-date, and is the background to the development of a new law concerning financial advising which come into force the 1th of July 2004. The contents of the thesis can be described as three bricks, representing the survey questions. The thesis starts with descriptions of which risk- and return concepts that exists and which are used by the contemporary financial institutions. Further on, the thesis deals with the individuals’ perception of risk, in particular financial risk. To end with, details regarding how a message should be conveyed are given. The three bricks together fulfil the purpose of the thesis; To investigate how the meaning of financial risk in a simple and pedagogical way can be explained to a person not familiar with financial literature, and to develop questions that facilitate when an individuals risk profile is ascertained. We have found that standard deviation is the risk concept that dominates in financial theory, and together with Value at Risk is the most common used in practise. Good knowledge about risk is required when explaining risk. It is important to describe the information in an attractive way and use examples and illustrations. For financial advisers it also is important to have knowledge about the human behaviour, because ascertain the clients risk profile is an important part of the risk explanation. A clients risk profile is best ascertain with so called open questions where both what the clients answer and how he or she answer can form the basis for the judgement.