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Statistical Modeling (statistical + modeling)

Distribution by Scientific Domains

Medical Sciences	50%
Mathematics and Statistics	16%

Selected Abstracts

The European NEAT Program: An Integrated Approach Using Acamprosate and Psychosocial Support for the Prevention of Relapse in Alcohol-Dependent Patients With a Statistical Modeling of Therapy Success Prediction

ALCOHOLISM, Issue 10 2002
Isidore Pelc
Background A multicenter, prospective study was conducted in five European countries to observe outcome in alcohol misusers treated for 24 weeks with acamprosate and various psychosocial support techniques, within the setting of standard patient care. Methods Patients diagnosed as alcohol dependent using DSM-III-R criteria were treated, for 24 weeks, with acamprosate and appropriate psychosocial support. Potential predictor variables were recorded at inclusion. Drinking behavior was monitored throughout; the proportion of cumulative abstinence days was the principal outcome measure. The influence of baseline clinical and demographic variables on outcome was assessed using multiple regression analysis. Adverse events were recorded systematically. Results A total of 1289 patients were recruited; 1230 took at least one dose of the drug and provided at least one set of follow-up data; 543 (42.1%)patients were observed for the full 24-week period. The overall proportion of cumulative abstinence days was 0.48. Multiple physical and psychiatric comorbidities and a history of drug addiction were negatively correlated with outcome, as were, to a lesser extent, multiple previous episodes of detoxification, unemployment, and living alone. Older age and stable employment were positively associated with outcome. The difference in the unadjusted proportion of cumulative abstinence days between countries was significant (p < 0.001) but less so when adjusted for the predictive factors identified in the multivariate model (p < 0.019). Overall, outcome was not influenced by the nature of the psychosocial support provided. Adverse events were generally mild, with gastrointestinal disorders, which occurred in 21.5% of patients, being the most frequent. Conclusions This open-label study confirms the efficacy and safety of acamprosate in the treatment of alcohol dependence in the setting of standard patient care. Treatment benefit was observed irrespective of the nature of the psychosocial support provided. Predictors of the response to treatment were identified; their heterogeneous distribution within the study population explained, at least in part, the differences in outcome between countries. [source]

Advances in Mathematical and Statistical Modeling edited by ARNOLD, B. C., BALAKRISHNAN, N., SARABIA, J. M. and MÍNGUEZ, R.

BIOMETRICS, Issue 2 2009
Article first published online: 28 MAY 200
No abstract is available for this article. [source]

Separable approximations of space-time covariance matrices

ENVIRONMETRICS, Issue 7 2007
Marc G. Genton
Abstract Statistical modeling of space-time data has often been based on separable covariance functions, that is, covariances that can be written as a product of a purely spatial covariance and a purely temporal covariance. The main reason is that the structure of separable covariances dramatically reduces the number of parameters in the covariance matrix and thus facilitates computational procedures for large space-time data sets. In this paper, we discuss separable approximations of nonseparable space-time covariance matrices. Specifically, we describe the nearest Kronecker product approximation, in the Frobenius norm, of a space-time covariance matrix. The algorithm is simple to implement and the solution preserves properties of the space-time covariance matrix, such as symmetry, positive definiteness, and other structures. The separable approximation allows for fast kriging of large space-time data sets. We present several illustrative examples based on an application to data of Irish wind speeds, showing that only small differences in prediction error arise while computational savings for large data sets can be obtained. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Does nicotine influence cytokine profile and subsequent cell cycling/apoptotic responses in inflammatory bowel disease?

INFLAMMATORY BOWEL DISEASES, Issue 11 2008
Marian C. Aldhous PhD
Abstract Background: Smoking differentially influences susceptibility to the inflammatory bowel diseases (IBDs) Crohn's disease (CD) and ulcerative colitis (UC). We investigated the effects of nicotine on cytokine, cell cycle, and apoptotic responses in peripheral blood mononuclear cells (PBMCs) from IBD patients and healthy controls (HCs). Methods: PBMCs from IBD patients and HC were stimulated with lipopolysaccharide (LPS; 1 ,g/mL) or phytohemagglutinin (PHA, 5 or 0.5 ,g/mL), ± nicotine (1, 10, 100 ,g/mL). Cytokines (IL1,, IL2, IL10, IL12/IL23p40, TGF,, TNF,) were measured in supernatants at 24 hours. After 72 hours cells were analyzed by flow cytometry for cell cycle and apoptosis. Statistical modeling was used to identify interactions between cytokines and cell cycle / apoptosis and minimize confounding effects. Results: Stimulation by LPS and PHA (5 ,g/mL) increased IL12/IL23p40 production from CD and UC versus HC (P < 0.05); PHA (0.5 ,g/mL) increased IL1, in UC and decreased TGF, from CD and UC (P < 0.01). In all groups, nicotine reduced LPS- and PHA (0.5 ,g/mL)-stimulated production of IL1,, IL10, TGF,, and TNF, (P < 0.001). Cell cycle analysis showed that PHA, but not LPS, induced proliferation and decreased G0/G1 resting cells in CD and UC versus HC (P < 0.001). Nicotine decreased PHA-stimulated S-phase proliferation and increased G0/G1 resting cells (P < 0.01). Modeling showed independent associations between IL12/IL23p40 and apoptosis (P = 0.01), IL1, and resting cells (P = 0.006), TNF, and proliferating cells (P < 0.001). Disease activity and smoking habit had no effect. Conclusions: Dysregulated cytokine profiles in UC and CD are associated with specific alterations in cell cycle responses; these effects may be modified by nicotine, and potentially by anticytokine therapies. (Inflamm Bowel Dis 2008) [source]

Computational modeling of tetrahydroimidazo-[4,5,1-jk][1,4]-benzodiazepinone derivatives: An atomistic drug design approach using Kier-Hall electrotopological state (E-state) indices

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2008
Nitin S. Sapre
Abstract Quantitative structure-activity relationships (QSAR), based on E-state indices have been developed for a series of tetrahydroimidazo-[4,5,1-jk]-benzodiazepinone derivatives against HIV-1 reverse transcriptase (HIV-1 RT). Statistical modeling using multiple linear regression technique in predicting the anti-HIV activity yielded a good correlation for the training set (R2 = 0.913, R = 0.897, Q2 = 0.849, MSE = 0.190, F -ratio = 59.97, PRESS = 18.05, SSE = 0.926, and p value = 0.00). Leave-one-out cross-validation also reaffirmed the predictions (R2 = 0.850, R = 0.824, Q2 = 0.849, MSE = 0.328, and PRESS = 18.05). The predictive ability of the training set was also cross-validated by a test set (R2 = 0.812, R = 0.799, Q2 = 0.765, MSE = 0.347, F -ratio = 64.69, PRESS = 7.37, SSE = 0.975, and p value = 0.00), which ascertained a satisfactory quality of fit. The results reflect the substitution pattern and suggest that the presence of a bulky and electropositive group in the five-member ring and electron withdrawing groups in the seven-member ring will have a positive impact on the antiviral activity of the derivatives. Bulky groups in the six-member ring do not show an activity-enhancing impact. Outlier analysis too reconfirms our findings. The E-state descriptors indicate their importance in quantifying the electronic characteristics of a molecule and thus can be used in chemical interpretation of electronic and steric factors affecting the biological activity of compounds. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]

Clutter reduction in synthetic aperture radar images with statistical modeling: An application to MSTAR data

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2008
Sevket Demirci
Abstract In this article, an application of clutter modeling and reduction techniques to synthetic aperture radar (SAR) images of moving and stationary target acquisition and recognition data is presented. Statistical modeling of the clutter signal within these particular SAR images is demonstrated. Lognormal, Weibull, and K-distribution models are analyzed for the amplitude distribution of high-resolution land clutter data. Higher-order statistics (moments and cumulants) are utilized to estimate the appropriate statistical distribution models for the clutter. Also, Kolmogorov-Smirnov (K-S) goodness-of-fit test is employed to validate the accuracy of the selected models. With the use of the determined clutter model, constant false-alarm rate detection algorithm is applied to the SAR images of several military targets. Resultant SAR images obtained by using the proposed method show that target signatures are reliably differentiated from the clutter background. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1514,1520, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23413 [source]

Secular Trends in the Incidence of Female Breast Cancer in the United States, 1973,1998

THE BREAST JOURNAL, Issue 2 2004
Kiumarss Nasseri DVM
Abstract: , Statistical modeling suggests a causal association between the rapid increase in the incidence of female breast cancer (FBC) in the United States and the widespread use of screening mammography. Additional support for this suggestion is a shift in the stage at diagnosis that consists of an increase in early stage diagnosis followed by a decrease in late-stage diagnosis. This has not been reported in the United States. The objective of this study was to examine the secular trends in the incidence of FBC in search of empirical support for this shift. FBC cases in the Surveillance, Epidemiology, and End Results (SEER) database from 1973 through 1998 were dichotomized into early and late detection based. Early detection included all the in situ and invasive cases with local spread. Late detection included cases with regional spread and distant metastasis. Joinpoint segmented regression modeling was used for trend analysis. Early detection in white and black women followed a similar pattern of significant increase in the early 1980s that continued through 1998 with slight modification in 1987. The expected shift in stage was noticed only for white women when the incidence of late detection in them began to decline in 1987. The incidence of late detection in black women has remained stable. These results provide further support for the previously implied causal association between the use of screening mammography and the increased incidence of FBC in the United States. It also shows that the expected stage shift appeared in white women 50,69 years of age after an estimated detection lead time (DLT) of about 5 years. This is the first estimate of DLT in the United States that is based on actual data. The subsequent increase in late detection in white women since 1993 may be due to changes in case management and the increased use of sentinel lymph node biopsy (SLNB) rather than changes in the etiology or biology of FBC., [source]

Quantitative Trait Loci for BMD in an SM/J by NZB/BlNJ Intercross Population and Identification of Trps1 as a Probable Candidate Gene,,

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2008
Naoki Ishimori
Abstract Identification of genes that regulate BMD will enhance our understanding of osteoporosis and could provide novel molecular targets for treatment or prevention. We generated a mouse intercross population and carried out a quantitative trait locus (QTL) analysis of 143 female and 124 male F2 progeny from progenitor strains SM/J and NZB/BlNJ using whole body and vertebral areal BMD (aBMD) as measured by DXA. We found that both whole body and vertebral aBMD was affected by two loci on chromosome 9: one with a significant epistatic interaction on distal chromosome 8 and the other with a sex-specific effect. Two additional significant QTLs were identified on chromosome 12, and several suggestive ones were identified on chromosomes 5, 8, 15, and 19. The chromosome 9, 12, and 15 loci have been previously identified in other crosses. SNP-based haplotype analysis of the progenitor strains identified blocks within the QTL region that distinguish the low allele strains from the high allele strains, significantly narrowing the QTL region and reducing the possible candidate genes to 98 for chromosome 9, 31 for chromosome 12, and only 2 for chromosome 15. Trps1 is the most probable candidate gene for the chromosome 15 QTL. The sex-specific effects may help to elucidate the BMD differences between males and females. This study shows the power of statistical modeling to resolve linked QTLs and the use of haplotype analysis in narrowing the list of candidates. [source]

Distribution of Patients, Paroxysmal Atrial Tachyarrhythmia Episodes: Implications for Detection of Treatment Efficacy

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2 2001
WILLIAM F. KAEMMERER Ph.D.
Distribution of Paroxysmal Atrial Tachyarrhythmia Episodes.Introduction: Clinical trials of treatments for paroxysmal atrial tachyarrhythmia (pAT) often compare different treatment groups using the time to first episode recurrence. This approach assumes that the time to the first recurrence is representative of all times between successive episodes in a given patient. We subjected this assumption to an empiric test. Methods and Results: Records of pAT onsets from a chronologic series of 134 patients with dual chamber implantable defibrillators were analyzed; 14 had experienced > 10 pAT episodes, which is sufficient for meaningful statistical modeling of the time intervals between episodes. Episodes were independent and randomly distributed in 9 of 14 patients, but a fit of the data to an exponential distribution, required by the stated assumption, was rejected in 13 of 14. In contrast, a Weibull distribution yielded an adequate goodness of fit in 5 of the 9 cases with independent and randomly distributed data. Monte Carlo methods were used to determine the impact of violations of the exponential distribution assumption on clinical trials using time from cardioversion to first episode recurrence as the dependent measure. In a parallel groups design, substantial loss of power occurs with sample sizes < 500 patients per group. In a cross-over design, there is insufficient power to detect a 30% reduction in episode frequency even with 300 patients. Conclusion: Clinical trials that rely on time to first episode recurrence may be considerably less able to detect efficacious treatments than may have been supposed. Analysis of multiple episode onsets recorded over time should be used to avoid this pitfall. [source]

Linking program implementation and effectiveness: Lessons from a pooled sample of welfare-to-work experiments

JOURNAL OF POLICY ANALYSIS AND MANAGEMENT, Issue 4 2003
Howard S. Bloom
This paper addresses the question: How does implementation influence the effectiveness of mandatory welfare-to-work programs? Data from three large-scale, multi-site random assignment experiments were pooled; quantitative measures of program implementation were constructed; and multilevel statistical modeling was used to examine the relationship between program implementation and effects on short-term client earnings. Individual-level data were analyzed for 69,399 sample members and group-level implementation data were analyzed for 59 local programs. Findings indicate that, other things being equal, earnings effects are increased by: an emphasis on quick client employment, an emphasis on personalized client attention, staff caseloads that do not get too large, and limited use of basic education. Findings also show that mandatory welfare-to-work programs can be effective for many types of people, and that focusing on clients who are especially job-ready (or not) does not have a consistent influence on a program's effectiveness. © 2003 by the Association for Public Policy Analysis and Management [source]

Clutter reduction in synthetic aperture radar images with statistical modeling: An application to MSTAR data

Could accelerated aging explain the excess mortality in patients with seropositive rheumatoid arthritis?

ARTHRITIS & RHEUMATISM, Issue 2 2010
Cynthia S. Crowson
Objective To determine whether the mortality pattern in patients with seropositive rheumatoid arthritis (RA) is consistent with the concept of accelerated aging, by comparing the observed mortality rates in patients with RA with the age-accelerated mortality rates from the general population. Methods A population-based inception cohort of patients with seropositive RA (according to the American College of Rheumatology 1987 criteria) was assembled and followed up for vital status until July 1, 2008. The expected mortality rate was obtained by applying the death rates from the general population to the age, sex, and calendar year distribution of the RA population. The observed mortality was estimated using Kaplan-Meier methods. Acceleration factors for the expected mortality were estimated in accelerated failure time models. Results A total of 755 patients with seropositive RA (mean age 55.6 years, 69% women) were followed up for a mean of 12.5 years, during which 315 patients died. The expected median survival was age 82.4 years, whereas the median survival of the RA patients was age 76.7 years. Results of statistical modeling suggested that, in terms of mortality rates, patients with RA were effectively 2 years older than actual age at RA incidence, and thereafter the patients underwent 11.4 effective years of aging for each 10 years of calendar time. Conclusion The overall observed mortality experience of patients with seropositive RA is consistent with the hypothesis of accelerated aging. The causes of accelerated aging in RA deserve further investigation. [source]