| 1. |
- Ahmad, M. Rauf, et al.
(författare)
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A U-classifier for high-dimensional data under non-normality
- 2018
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Ingår i: Journal of Multivariate Analysis. - Uppsala Univ, Dept Stat, Uppsala, Sweden. KTH, Royal Inst Technol, Dept Math, Stockholm, Sweden. : ELSEVIER INC. - 0047-259X .- 1095-7243. ; 167, s. 269-283
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Tidskriftsartikel (refereegranskat)abstract
- A classifier for two or more samples is proposed when the data are high-dimensional and the distributions may be non-normal. The classifier is constructed as a linear combination of two easily computable and interpretable components, the U-component and the P-component. The U-component is a linear combination of U-statistics of bilinear forms of pairwise distinct vectors from independent samples. The P-component, the discriminant score, is a function of the projection of the U-component on the observation to be classified. Together, the two components constitute an inherently bias-adjusted classifier valid for high-dimensional data. The classifier is linear but its linearity does not rest on the assumption of homoscedasticity. Properties of the classifier and its normal limit are given under mild conditions. Misclassification errors and asymptotic properties of their empirical counterparts are discussed. Simulation results are used to show the accuracy of the proposed classifier for small or moderate sample sizes and large dimensions. Applications involving real data sets are also included.
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| 2. |
- Appelberg, Jonas, 1964-, et al.
(författare)
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Lung aeration during sleep
- 2007
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Ingår i: Chest. - : Elsevier BV. - 0012-3692 .- 1931-3543. ; 131:1, s. 122-129
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Tidskriftsartikel (refereegranskat)abstract
- Background: During sleep, ventilation and functional residual capacity (FRC) decrease slightly. This study addresses regional lung aeration during wakefulness and sleep. Methods: Ten healthy subjects underwent spirometry awake and with polysomnography, including pulse oximetry, and also CT when awake and during sleep. Lung aeration in different lung regions was analyzed. Another three subjects were studied awake to develop a protocol for dynamic CT scanning during breathing. Results: Aeration in the dorsal, dependent lung region decreased from a mean of 1.14 ± 0.34 mL (± SD) of gas per gram of lung tissue during wakefulness to 1.04 ± 0.29 mL/g during non-rapid eye movement (NREM) sleep (- 9%) [p = 0.034]. In contrast, aeration increased in the most ventral, nondependent lung region, from 3.52 ± 0.77 to 3.73 ± 0.83 mL/g (+ 6%) [p = 0.007]. In one subject studied during rapid eye movement (REM) sleep, aeration decreased from 0.84 to 0.65 mL/g (- 23%). The fall in dorsal lung aeration during sleep correlated to awake FRC (R2 = 0.60; p = 0.008). Airway closure, measured awake, occurred near and sometimes above the FRC level. Ventilation tended to be larger in dependent, dorsal lung regions, both awake and during sleep (upper region vs lower region, 3.8% vs 4.9% awake, p = 0.16, and 4.5% vs 5.5% asleep, p = 0.09, respectively). Conclusions: Aeration is reduced in dependent lung regions and increased in ventral regions during NREM and REM sleep. Ventilation was more uniformly distributed between upper and lower lung regions than has previously been reported in awake, upright subjects. Reduced respiratory muscle tone and airway closure are likely causative factors.
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| 3. |
- Appelberg, Jonas, 1964-, et al.
(författare)
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Lung aeration during sleep in patients with obstructive sleep apnoea
- 2010
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Ingår i: Clinical Physiology and Functional Imaging. - Oxford : Blackwell Publishing. - 1475-0961 .- 1475-097X. ; 30:4, s. 301-307
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Tidskriftsartikel (refereegranskat)abstract
- P>Background: Previous studies have indicated that patients with obstructive sleep apnoea (OSA) have altered ventilation and lung volumes awake and the results suggest that this may be a determinant of severity of desaturations during sleep. However, little is known about regional lung aeration during sleep in patients with OSA. Methods: Twelve patients with OSA were included in the study. Computed tomography was used to study regional lung aeration during wakefulness and sleep. Lung aeration was calculated in ml gas/g lung tissue in four different regions of interest (ROI1-4), along the border of the lung from ventral to dorsal. Results: Lung aeration in the dorsal (dependent) lung region (ROI4) was lower during sleep compared to wakefulness 0 center dot 78 +/- 0 center dot 19 versus 0 center dot 88 +/- 0 center dot 19 (mean +/- SD) ml gas/g lung tissue (P = 0 center dot 005). Associations were found between awake expiratory reserve volume and change in lung aeration from wakefulness to sleep in ROI4 (r = -0 center dot 69; P = 0 center dot 012). In addition, the change in lung aeration in the dorsal region correlated to sleep time (r = 0 center dot 69; P = 0 center dot 014) but not to time in supine position. The difference in lung aeration between inspiration and expiration (i.e. ventilation), was larger in the ventral lung region when expressed as ml gas per g lung tissue. In two patients it was noted that, during on-going obstructive apnoea, lung aeration tended to be increased rather than decreased. Conclusions: Aeration in the dorsal lung region is reduced during sleep in patients with OSA. The decrease is related to lung volume awake and to sleep time.
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| 4. |
- Corander, Jukka, et al.
(författare)
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Bayesian Block-Diagonal Predictive Classifier for Gaussian Data
- 2013
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Ingår i: Synergies of Soft Computing and Statistics for Intelligent Data Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642330414 - 9783642330421 ; , s. 543-551
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Bokkapitel (refereegranskat)abstract
- The paper presents a method for constructing Bayesian predictive classifier in a high-dimensional setting. Given that classes are represented by Gaussian distributions with block-structured covariance matrix, a closed form expression for the posterior predictive distribution of the data is established. Due to factorization of this distribution, the resulting Bayesian predictive and marginal classifier provides an efficient solution to the high-dimensional problem by splitting it into smaller tractable problems. In a simulation study we show that the suggested classifier outperforms several alternative algorithms such as linear discriminant analysis based on block-wise inverse covariance estimators and the shrunken centroids regularized discriminant analysis.
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| 5. |
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| 6. |
- Dorfman, M.V, et al.
(författare)
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Questionnaire-based determination of groups at high risk for lung cancer (in Russian)
- 1990
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Ingår i: Problems of Oncology (rus). - 0507-3758. ; 36:12, s. 1469-1473
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Tidskriftsartikel (refereegranskat)abstract
- The factor analysis of qualitative parameters carried out in 968 patients with lung cancer helped identify certain features which may play the key role in the development and, consequently, diagnosis of various types of the disease. In workers of major industries, smoking proved a significant factor of higher incidence of lung cancer. Formation of the habit at an earlier age, its intensity and concomitant occupational hazards were found to increase the risk of cancer, particularly, in males. Mass screenings and questionnaire--based interviewing of smokers are suggested. Young age and heavy smokers should be included in groups at risk irrespective of
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| 7. |
- Duras, Toni
(författare)
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Applications of common principal components in multivariate and high-dimensional analysis
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of four papers, all exploring some aspect of common principal component analysis (CPCA), the generalization of PCA to multiple groups. The basic assumption of the CPC model is that the space spanned by the eigenvectors is identical across several groups, whereas eigenvalues associated with the eigenvectors can vary. CPCA is used in essentially the same areas and applications as PCA.The first paper compares the performance of the maximum likelihood and Krzanowski’s estimators of the CPC model for two real-world datasets and in a Monte Carlo simulation study. The simplicity and intuition of Krzanowski's estimator and the findings in this paper support and promote the use of this estimator for CPC models over the maximum likelihood estimator.Paper number two uses CPCA as a tool for imposing restrictions on system-wise regression models. The paper contributes to the field by proposing a variety of explicit estimators, deriving their properties and identifying the appropriate amount of smoothing that should be imposed on the estimator. In the third paper, a generalization of the fixed effects PCA model to multiple populations in a CPC environment is proposed. The model includes mainly geometrical, rather than probabilistic, assumptions, and is designed to account for any possible prior information about the noise in the data to yield better estimates, obtained by minimizing a least squares criterion with respect to a specified metric.The fourth paper survey some properties of the orthogonal group and the associated Haar measure on it. It is demonstrated how seemingly abstract results contribute to applied statistics and, in particular, to PCA.
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| 8. |
- Fomina, Svitlana, et al.
(författare)
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Clinical course of steroid sensitive nephrotic syndrome in children: outcome and outlook
- 2011
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Ingår i: The Open Pediatric Medicine Journal. - : Bentham Science Publishers Ltd.. - 1874-3099. ; 5, s. 18-28
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: The aim of our study was to investigate the relative efficiency and adverse effects of various treatments of steroid sensitive nephrotic syndrome (SSNS) in children, and to determine factors associated with relapse risk in these patients. Materials and Method: We retrospectively studied the data from 690 SSNS children treated in referral center over 25 years. The analyzed treatment protocols were: Prednisolone (PRED, eight weeks in a dose 1.5-2.0 mg/kg, then it tapering and given for 9-12 months), Chlorambucil (CHL, cumulative dose 28.5-30 mg/kg), Cyclophosphamide intravenously (CYC I.V., cumulative dose of 30-36 mg/kg, then supporting dose of CHL, cumulative dose of 20-25 mg/kg) and intramuscular (CYC I.M., cumulative dose of 120-150 mg/kg). The alkylating agents were used after remission induction by PRED and under its protection. Results: Cumulative relapse-free survival was 81.9%, 69.0% and 64.5% after 12, 36 and 60 months, respectively. In multivariate analyses, relapse risk was associated with age of treatment (<6 years), and both PRED and CYC I.V. The only predictive factor for early relapse was PRED, unlike two and more relapses group where PRED and CYC I.V. as well as age from 3 to 6 years was highly prognostic. The high probability of sustained remission in combination with relatively mild adverse effects was observed for PRED used at first episode and CHL used at relapse. Conclusion: To summarize, our protocols characterized by the prolonged PRED and CHL demonstrated promising results and should be considered as an efficient alternative strategy in SSNS management.
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| 9. |
- Fomina, Svitlana, et al.
(författare)
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Clinical patterns and renal survival of nephrotic syndrome in childhood : a single-center study (1980-2006)
- 2010
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Ingår i: The open urology & nephrology journal. - 1874-303X. ; 3, s. 8-15
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Tidskriftsartikel (refereegranskat)abstract
- To investigate changes in the diagnostic patterns, disease profiles courses and therapeutic strategies for severe forms of childhood nephrotic syndrome (NS), the clinical features of 1 349 children treated during two consecutive time periods, 1980-2000 (n=1 162) and 2001-2006 (n=187), were retrospectively reviewed. The significant increase in initial renal impairment, NS with hypertension, and NS with hypertension and hematuria was observed (27.7% vs 51.3%, 1.0% vs 5.3% and 16.4% vs 21.9%, respectively). The rate of both secondary steroid resistance (SR) and Focal Segmental Glomerulosclerosis increased significantly, (1.8% vs 5.6%, p=0.032, and 14.9% vs 29.0%, p=0.034, respectively). The initial renal insufficiency and hypertension were highly predictive of the development of stage 3 of chronic kidney disease (CKD3) among SR patients in a multivariate Cox regression (p=0.001) for years 1980-2000. A higher hazard of CKD3 in male SR patients from three to six years old was observed in 2001-2006. Kaplan-Meier survival curves revealed a shift in the cumulative probability of CKD3, indicating a slower decline of the renal function for SR NS in the years 2001-2006 (p=0.008): the estimated five-year CKD3 risk was 39.7% vs 27.7%. Achievements in inducing remission and retarding the development of CKD3 in combination with increased severity of NS indicate the effectiveness of domestic strategies of NS management.
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