20 research outputs found

    Moment Tests for Window Length Selection in Singular Spectrum Analysis of Short- and Long-Memory Processes

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    In this paper we propose a new methodology for selecting the window length in Singular Spectral Analysis in which the window length is determined from the data prior to the commencement of modeling. The selection procedure is based on statistical tests designed to test the convergence of the autocovariance function. A classical time series portmanteau type statistic and two test statistics derived using a conditional moment principle are considered. The first two are applicable to short-memory processes, and the third is applicable to both short- and long-memory processes. We derive the asymptotic distribution of the statistics under fairly general regularity conditions and show that the criteria will identify true convergence with a finite window length with probability one as the sample size increases. Results obtained using Monte-Carlo simulation indicate the relevance of the asymptotic theory, even in relatively small samples, and that the conditional moment tests will choose a window length consistent with the Whitney embedding theorem. Application to observations on the Southern Oscillation Index shows how observed experimental behaviour can be reflected in features seen with real world data sets.Portmanteau type test, Conditional moment test, Asymptotic distribution, Linear regular process, Singular spectrum analysis, Embedding

    Description Length Based Signal Detection in singular Spectrum Analysis

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    This paper provides an information theoretic analysis of the signal-noise separation problem in Singular Spectrum Analysis. We present a signal-plus-noise model based on the Karhunen-Loève expansion and use this model to motivate the construction of a minimum description length criterion that can be employed to select both the window length and the signal. We show that under very general regularity conditions the criterion will identify the true signal dimension with probability one as the sample size increases, and will choose the smallest window length consistent with the Whitney embedding theorem. Empirical results obtained using simulated and real world data sets indicate that the asymptotic theory is reflected in observed behaviour, even in relatively small samples.Karhunen-Loève expansion, minimum description length, signal-plus-noise model, Singular Spectrum Analysis, embedding

    Window Length Selection and Signal-Noise Separation and Reconstruction in Singular Spectrum Analysis

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    In Singular Spectrum Analysis (SSA) window length is a critical tuning parameter that must be assigned by the practitioner. This paper provides a theoretical analysis of signal-noise separation and reconstruction in SSA that can serve as a guide to optimal window choice. We establish numerical bounds on the mean squared reconstruction error and present their almost sure limits under very general regularity conditions on the underlying data generating mechanism. We also provide asymptotic bounds for the mean squared separation error. Evidence obtained using simulation experiments indicates that the theoretical properties are reflected in observed behaviour, even in relatively small samples, and the results indicate how an optimal choice for the window length can be made.Dimension, Embedding, Mean squared error, Reconstruction, Signal-noise separation, Window length.

    Statistical Analysis of a Time-course Nasopharyngeal Carcinoma Gene Expression Data.

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    Master'sMASTER OF SCIENC

    Posterior lumber interbody fusion with pedicle screw fixation for the management of spondylolisthesis: An analysis of 40 cases

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    Spondylolisthesis is forward slipping of upper vertebra in relations to its lower one, commonest is L4-L5. The ideal surgical treatment of spondylolisthesis is still controversial. Posterior lumber interbody fusion with pedicle fixation is one of treatment choices for the lumber spondylolisthesis. Forty patients who operated through posterior lumber interbody fusion and pedicle screw fixation by single surgeon was included from January 2012 to March 2015. Periodical follow-up was done both clinically and radiologically up to 6 months. Patient outcome was completed based on pain relief graphic rating scale and Oswestry disability index. In our series, the excellent outcome were 25 patients (62.5%), good were 12 patients (30%), and fair were 3 patients (7.5%). There were no poor outcome and no new neurological deficit. This study concludes that posterior lumber inter-body fusion with pedicle is an effective treatment for the lumber spondylolisthesis. It helps to maintain the biomechanics, associated with less complication and improve the quality of life of patient

    Stealth cranioplasty in symptomatic adult chiari 1 malformations: Experience at Bangabandhu Sheikh Mujib Medical University

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    Background: The surgical management of symptomatic adult Chiari malformation type 1 (CM1) with or without syringomyelia (SM) continues to be a dilemma considering the outcomes. Objectives: The study aimed to compare the clinical outcomes between stealth cranioplasty (SC) and one of the most commonly practiced standard procedures, posterior fossa decompression with duraplasty (PFDD). Clinical outcomes between SC and another procedure posterior fossa decompression (PFD) were also compared. Methods: This comparative cross-sectional study was carried out on 37 males and 16 females symptomatic adult CM1 patients, ranging from 18 to 47 years of age from June 2019 to May 2021. Clinical outcomes were assessed, compared, and analyzed in terms of changes in clinical symptoms and signs, chicago chiari outcome scale (CCOS) score, and occurrence of complications.  Results: Of the 53 patients, 23, 19 and 11 underwent SC, PFDD, and PFD, respectively. There were no significant post-operative changes in symptoms and signs among groups except changes in limb weakness between SC and PFDD (P=0.004). Considering average CCOS score, SC performed better only than PFDD (P=0.003), while category-wise SC was better than both PFDD (P=0.004) and PFD (P=0.010). Considering complications, the PFDD group had a significantly higher rate of complications than the SC group (P=0.001), while there was no significant difference in the rate of complications between the PFD and SC groups. Conclusion: SC was found to have better clinical outcomes than the PFDD and PFD groups as a technique. Bangabandhu Sheikh Mujib Medical University Journal 2023;16(1): 08-1

    Stealth cranioplasty in symptomatic adult chiari 1 malformations: Experience at Bangabandhu Sheikh Mujib Medical University

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    Background: The surgical management of symptomatic adult Chiari malformation type 1 (CM1) with or without syringomyelia (SM) continues to be a dilemma considering the outcomes. Objectives: The study aimed to compare the clinical outcomes between stealth cranioplasty (SC) and one of the most commonly practiced standard procedures, posterior fossa decompression with duraplasty (PFDD). Clinical outcomes between SC and another procedure posterior fossa decompression (PFD) were also compared. Methods: This comparative cross-sectional study was carried out on 37 males and 16 females symptomatic adult CM1 patients, ranging from 18 to 47 years of age from June 2019 to May 2021. Clinical outcomes were assessed, compared, and analyzed in terms of changes in clinical symptoms and signs, chicago chiari outcome scale (CCOS) score, and occurrence of complications.  Results: Of the 53 patients, 23, 19 and 11 underwent SC, PFDD, and PFD, respectively. There were no significant post-operative changes in symptoms and signs among groups except changes in limb weakness between SC and PFDD (P=0.004). Considering average CCOS score, SC performed better only than PFDD (P=0.003), while category-wise SC was better than both PFDD (P=0.004) and PFD (P=0.010). Considering complications, the PFDD group had a significantly higher rate of complications than the SC group (P=0.001), while there was no significant difference in the rate of complications between the PFD and SC groups. Conclusion: SC was found to have better clinical outcomes than the PFDD and PFD groups as a technique. Bangabandhu Sheikh Mujib Medical University Journal 2023;16(1): 08-1

    Financial threat, hardship and distress predict depression, anxiety and stress among the unemployed youths: a Bangladeshi multi-cities study

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    Introduction: Unemployment has a contributory role in the development of mental health problems and in Bangladesh there is increasing unemployment, particularly among youth. Consequently, the present study investigated depression, anxiety, and stress among recent graduates in a multi-city study across the country. Methods: A cross-sectional study was conducted among 988 Bangladeshi graduate jobseekers in six major cities of the country between August to November 2019. The measures included socio-demographics and life-style factors, study and job-related information, Economic Hardship Questionnaire, Financial Threat Scale, Financial Well-Being Scale, and Depression Anxiety Stress Scale-21. Results: Depression, anxiety and stress rates among the present sample were 81.1% (n=801), 61.5% (n=608) and 64.8% (n=640) respectively. Factors related to gender, age, socio-economic conditions, educational background, lack of extra-curricular activities, and high screen activity were significant risk factors of depression, anxiety, and stress. Structural equation modeling indicated that (while controlling for age, daily time spent on sleep study, and social media use), financial threat was moderately positively related to depression, anxiety, and stress. Financial hardship was weakly positively associated with depression, anxiety, and stress, whereas financial wellbeing was weakly negatively associated with depression, anxiety, and stress. Limitations: Due to the nature of the present study (i.e., cross-sectional study) and sampling method (i.e., convenience sampling), determining causality between the variables is not possible. Conclusions: The present results emphasized the important detrimental role of financial troubles on young people's mental health by showing that financial problems among unemployed youth predict elevated psychiatric distress in both men and women

    Window Length Selection and Signal–Noise Separation and Reconstruction in Singular Spectrum Analysis

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    In Singular Spectrum Analysis (SSA) window length is a critical tuning parameter that must be assigned by the practitioner. This paper provides a theoretical analysis of signal-noise separation and reconstruction in SSA that can serve as a guide to optimal window choice. We establish numerical bounds on the mean squared reconstruction error and present their almost sure limits under very general regularity conditions on the underlying data generating mechanism. We also provide asymptotic bounds for the mean squared separation error. Evidence obtained using simulation experiments indicates that the theoretical properties are reflected in observed behaviour, even in relatively small samples, and the results indicate how an optimal choice for the window length can be made
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