Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Multivariate statistics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,153 records · Page 64Linked to original sources
PubMed2006

The prevalence of and variables associated with smoking in children and adolescents.

OBJECTIVE: To identify the prevalence of smoking and the presence of variables associated with the habit in children and adolescents of both sexes, aged 7 to 17 years, resident in the city of Maceió. METHODS: A cross-sectional epidemiological study of the student population of the both private and public education systems at elementary and high school level. Sample size was calculated based on the minimum predicted prevalence of a large number of variables, including smoking itself. Cluster sampling was employed. A questionnaire on smoking habits was completed during individual interviews with each student. Children who admitted having smoked on 1 or more day during the previous 30 were defined as current smokers. The variables analyzed were related to: the students (age, sex, previous experimentation with cigarettes and paid employment), their educational status (public/private school, daytime/evening lessons, grade and repeated years) and their families (economic status, smoking parents and separated parents). RESULTS: A total of 1,253 students were analyzed (547 were male, mean age was 12.4+/-2.9 years). Observed smoking prevalence was 2.4%. Multivariate statistical analysis demonstrated significant associations between smoking and: increased age (odds ratio: 1.31); previous experimentation with cigarettes (odds ratio: 33.96); studying during the evening (odds ratio: 5.43). It was observed that 286 students (22.8%) admitted having experimented with cigarettes (9% from 7 to 9 years; 21% from 10 to 14 years; 36% from 15 to 17 years). CONCLUSIONS: The prevalence of smoking among children and adolescents in the Maceió educational system is 2.4%, being most common among students aged 15 to 17 years, studying in the evening. Students who had experimented with cigarettes exhibited a 34 times greater chance of becoming smokers.

Adolescent↗
PubMed1998

Predictive factors for rupture of thoracoabdominal aortic aneurysm.

PURPOSE: To identify the predictive risk factors for rupture of thoracoabdominal aortic aneurysms (TAA). METHODS: Thirty-one patients with TAA who did not have the indications for surgical repair of the aneurysm were selected. Inclusion criteria were maximum diameter less than 60 mm, refusal of surgical treatment, and high surgical risk. The selected patients participated in a prospective follow-up study for a median period of 47 months and underwent at least two thoracoabdominal computed tomographic scans a year to measure transverse and anteroposterior diameters. Identification of the predictive factors associated with rupture was undertaken with multivariate analysis by means of Cox regression model. RESULTS: During the study period five patients underwent elective repair, six died of unrelated causes, nine had aneurysms that ruptured (all with diameters greater than 50 mm), and 11 reached the end of the study without rupture or surgical management. Initial anteroposterior diameter and annual growth rate of the anteroposterior diameter were the variables associated with rupture of the TAA according to the multivariate statistical analysis by means of Cox regression model. CONCLUSION: We recommend elective repair for a fit patient with asymptomatic TAA with an initial anteroposterior diameter of 50 mm only when there is an annual growth rate of at least 10 mm. Patients with similar diameters but with smaller annual growth rates should be treated conservatively and undergo thoracoabdominal computed tomography every 6 months. Patients with an initial anteroposterior diameter of 60 mm and an annual growth rate of 6 mm should undergo surgical treatment. These guidelines for elective repair of TAA are based on the results of a relatively small series and have to be carefully individualized for each patient.

Aged↗
PubMed2003

Bioprocess control from a multivariate process trajectory.

A multivariate bioprocess control approach, capable of tracking a pre-set process trajectory correlated to the biomass or product concentration in the bioprocess is described. The trajectory was either a latent variable derived from multivariate statistical process monitoring (MSPC) based on partial least squares (PLS) modeling, or the absolute value of the process variable. In the control algorithm the substrate feed pump rate was calculated from on-line analyzer data. The only parameters needed were the substrate feed concentration and the substrate yield of the growth-limiting substrate. On-line near-infrared spectroscopy data were used to demonstrate the performance of the control algorithm on an Escherichia coli fed-batch cultivation for tryptophan production. The controller showed good ability to track a defined biomass trajectory during varying process dynamics. The robustness of the control was high, despite significant external disturbances on the cultivation and control parameters.

Algorithms↗
PubMed2002

Outcome of penicillin-nonsusceptible Streptococcus pneumoniae meningitis: a nested case-control study.

BACKGROUND: There are few data comparing the clinical features, management and outcome of penicillin-nonsusceptible (PNSP) meningitis patients with penicillin-susceptible (PSSP) meningitis patients. METHODS: We performed a retrospective, nested case-control study comparing cases with PNSP meningitis with controls with PSSP meningitis obtained from the Immunization Monitoring Program, Active (IMPACT) cross-Canada surveillance study of invasive infections. RESULTS: There were 30 PNSP meningitis cases (10.1% of total) and 45 PSSP meningitis controls from 6 centers obtained from 297 meningitis cases in the IMPACT database from 1991 through 1999. Vancomycin was used for empiric therapy in no cases and controls in 1991 to 1993 and in all cases in 1999. A third generation cephalosporin was used in 93.3% of confirmed PNSP cases, and 70.0% also received vancomycin and/or rifampin. Penicillin was used in 66.7% of confirmed PSSP cases. PNSP cases were more likely than PSSP controls to have a second lumbar puncture (odds ratio, 4.1; P= 0.01). PNSP cases were treated with intravenous antibiotics for an average of 15.6 days compared with 12.3 days for controls ( P= 0.04). Among PNSP cases, those patients who did not receive empiric vancomycin were treated with intravenous antibiotics for an average of 18.5 days compared with 12.0 days for those who did receive empiric vancomycin ( P= 0.04). The overall mortality was 5.3%, and 36.6% of survivors had >or=1 neurologic sequelae, including 19.7% with hearing loss. In multivariate statistical models, PNSP was not a risk factor for intensive care unit admission or neurologic sequelae. CONCLUSIONS: Management of suspected bacterial meningitis and confirmed meningitis in Canadian children changed in the past decade. Treatment of PNSP meningitis is significantly different from that for PSSP meningitis. These changes have occurred in response to the emergence of PNSP in Canada. Neurologic sequelae remain common after meningitis, but there are no differences between PNSP cases and PSSP cases.

Adolescent↗
PubMed2001

Temporal population code of concurrent vocal signals in the auditory midbrain.

Unique patterns of spike activity across neuron populations have been implicated in the coding of complex sensory stimuli. Delineating the patterns of neural activity in response to varying stimulus parameters and their relationships to the tuning characteristics of individual neurons is essential to ascertaining the nature of population coding within the brain. Here, we address these points in the midbrain coding of concurrent vocal signals of a sound-producing fish, the plainfin midshipman. Midshipman produce multiharmonic vocalizations which frequently overlap to produce beats. We used multivariate statistical analysis from single-unit recordings across multiple animals to assess the presence of a temporal population code. Our results show that distinct patterns of temporal activity emerge among midbrain neurons in response to concurrent signals that vary in their difference frequency. These patterns can serve to code beat difference frequencies. The patterns directly result from the differential temporal coding of difference frequency by individual neurons. Difference frequency encoding, based on temporal patterns of activity, could permit the segregation of concurrent vocal signals on time scales shorter than codes requiring averaging. Given the ubiquity across vertebrates of auditory midbrain tuning to the temporal structure of acoustic signals, a similar temporal population code is likely present in other species.

Animal Communication↗
PubMed2005

Detection of epithelial ovarian cancer using 1H-NMR-based metabonomics.

Currently available serum biomarkers are insufficiently reliable to distinguish patients with epithelial ovarian cancer (EOC) from healthy individuals. Metabonomics, the study of metabolic processes in biologic systems, is based on the use of (1)H-NMR spectroscopy and multivariate statistics for biochemical data generation and interpretation and may provide a characteristic fingerprint in disease. In an effort to examine the utility of the metabonomic approach for discriminating sera from women with EOC from healthy controls, we performed (1)H-NMR spectroscopic analysis on preoperative serum specimens obtained from 38 patients with EOC, 12 patients with benign ovarian cysts and 53 healthy women. After data reduction, we applied both unsupervised Principal Component Analysis (PCA) and supervised Soft Independent Modeling of Class Analogy (SIMCA) for pattern recognition. The sensitivity and specificity tradeoffs were summarized for each variable using the area under the receiver-operating characteristic (ROC) curve. In addition, we analyzed the regions of NMR spectra that most strongly influence separation of sera of EOC patients from healthy controls. PCA analysis allowed correct separation of all serum specimens from 38 patients with EOC (100%) from all of the 21 premenopausal normal samples (100%) and from all the sera from patients with benign ovarian disease (100%). In addition, it was possible to correctly separate 37 of 38 (97.4%) cancer specimens from 31 of 32 (97%) postmenopausal control sera. SIMCA analysis using the Cooman's plot demonstrated that sera classes from patients with EOC, benign ovarian cysts and the postmenopausal healthy controls did not share multivariate space, providing validation for the class separation. ROC analysis indicated that the sera from patients with and without disease could be identified with 100% sensitivity and specificity at the (1)H-NMR regions 2.77 parts per million (ppm) and 2.04 ppm from the origin (AUC of ROC curve = 1.0). In addition, the regression coefficients most influential for the EOC samples compared to postmenopausal controls lie around delta3.7 ppm (due mainly to sugar hydrogens). Other loadings most influential for the EOC samples lie around delta2.25 ppm and delta1.18 ppm. These findings indicate that (1)H-NMR metabonomic analysis of serum achieves complete separation of EOC patients from healthy controls. The metabonomic approach deserves further evaluation as a potential novel strategy for the early detection of epithelial ovarian cancer.

Adenocarcinoma, Clear Cell↗
PubMed1979

Spike separation in multiunit records: a multivariate analysis of spike descriptive parameters.

Variables describing unit discharges from multiunit extracellular records were treated, using multivariate statistical analysis for further automatic spike separation. A spike was described by 8 parameters (3 amplitude values, 3 time values and 2 slopes). These 8 parameters were summarized by 2 new independent factors, the principal components (PC). Examination of the 2 PCs from each spike allowed the observer to determine PC families corresponding to spike populations. From these the spikes were automatically classified. PC analysis showed groups of redundant parameters. Elimination of redundancy decreased the computing time without lowering the separation efficiency of the method. Three parameters turned out to be sufficient for spike discrimination: the maximum and the minimum amplitudes and the time between these. This agrees well with the physical basis of current propagation in the conducting medium, from the firing neurone to the recording electrode.

Action Potentials↗
PubMedDate not supplied

Risk factors and prognostic variables for survival of foals with radiographic evidence of pulmonary disease.

The medical records of 163 neonatal foals that had thoracic radiographs taken within 48 hours of admission to a referral hospital were reviewed. The objectives of this study were (1) to identify risk factors for the development of thoracic radiographic changes and (2) to identify prognostic indicators for survival in foals with radiographic evidence of pulmonary disease. Failure of transfer of passive immunity (IgG concentration < or = 400 mg/dL) was the only risk factor for radiographic evidence of respiratory disease identified by multivariate analysis. Hypoxemic patients (PaO2 < or = 60 mm Hg) were 4.9 times more likely to reveal radiographic abnormalities in a subset of foals for which arterial blood gas results were available. Foals with a serum creatinine concentration > 1.7 mg/dL upon presentation, dyspnea, and a history of dystocia were significantly more likely to die based on the multivariate statistical outcome analysis. An anion gap > or = 20 mEq/dL was strongly associated with nonsurvival in a subset of foals with arterial blood gas results. These hematologic and biochemical variables can be readily obtained during the initial evaluation of sick foals. The presence of a high anion gap appeared to have the greatest clinical impact and may be a useful prognostic indicator in foals with radiographic evidence of respiratory disease. In contrast, the majority of physical examination variables, including evaluation of tachypnea, abnormal respiratory sounds, fever, weakness, and milk reflux from the nares, which are usually obtained during the general respiratory evaluation of foals, were unrelated to outcome.

Acid-Base Equilibrium↗
PubMed1990

[Psychiatric symptom dimensions induced by work stress--an application of redundancy analysis].

The relationship between work stress estimated by a work stress questionnaire and several psychic symptoms estimated by a psychiatric symptom questionnaire was examined by redundancy analysis, which is a multivariate statistical technique to determine two sets of variables, one set being dependent on the other. Its aim is maximization of the explained variance of the dependent variables by the linear combination of the explanatory variables. The results showed that the depressive items had the largest loadings on the work stress variables, when the psychiatric symptom questionnaire was used as dependent variable and that the dullness dimension and the concentration difficulty dimension tended to have high loadings, when the same analysis was done using the subjective fatigue feeling questionnaire and the work stress questionnaire. We ascertained that these two fatigue symptom dimensions, especially the latter, are identical with the depression dimension in the psychiatric questionnaire. We concluded that work stress might induce a depressive state rather than other psychological or psychiatric states.

Depression↗
PubMedDate not supplied

Risk factors for complications in clean-contaminated head and neck surgical procedures.

BACKGROUND: Contamination of a head and neck surgical wound with oropharyngeal secretions has been shown to dramatically increase the incidence of wound complications. Appropriate perioperative antibiotic prophylaxis has significantly reduced contaminated wound infection rates in several previous reports. The current study examined multiple patient parameters to determine risk factors for all perioperative complications following clean-contaminated head and neck surgical procedures. METHODS: Retrospective review of medical records from 159 patients who underwent clean-contaminated major head and neck surgical procedures at the University of Washington between 1985 and 1991. More than 30 preoperative and operative parameters were evaluated, and all complications were recorded. The data were examined using a multivariate statistical analysis. RESULTS: An overall complication rate of 63% included 22% with wound infections (oro/pharyngocutaneous fistula or purulent drainage), 22% with other types of infections, and 51% with noninfectious complications. The overall perioperative mortality rate was 1.2% (two patients). Prior radiotherapy, operative time, perioperative transfusion, and flap reconstruction were all associated with a significantly higher overall complication rate (p < or = 0.05). Only prior radiotherapy therapy correlated with an increase in wound infection rate (p = 0.05). CONCLUSIONS: Prior radiotherapy significantly increases the risk of perioperative complications and wound infections following clean-contaminated head and neck surgical procedures. Other factors reflecting the complexity of the procedure also influence the overall complication rate.

Adult↗
PubMed1995

Health insurance coverage and use of services among low-income elders: does residence influence the relationship?

This research uses a nationally representative sample of 1,425 low-income elders from the 1987 National Medical Expenditure Survey (NMES) to assess the independent and interaction effects of health insurance coverage and residence on the use of seven health care services: doctor visits, visits to other personnel, telephone contact, emergency room visits, overnight hospital stays, outpatient visits, and prescription medicines. It is hypothesized that (a) elders without insurance to supplement Medicare; (b) those who lived in nonmetropolitan areas use fewer health services; and (c) insurance status and residence interact to influence use of health services, with nonmetropolitan elders using fewer services than those living in metropolitan areas, regardless of insurance type. Using multivariate statistical analyses with both main effects and interaction term models, the data indicate that the type of insurance that low-income elders have is associated with their use of health services, and that residence has only modest effect. Individuals who have Medicaid, and to a lesser extent private supplements, use services more frequently than do those without supplements. Finally, despite the hypothesis, residence does not interact with insurance status in influencing use of services; the relationship between insurance and use of services does not vary across area of residence. The data suggest that the ability to pay, rather than supply constraints associated with nonmetropolitan areas, are of primary importance in determining health care use among low-income elders.

Aged↗
PubMed1993

Improving the selection of patients for upper gastrointestinal endoscopy.

A retrospective study was undertaken to investigate how endoscopies yielding positive findings differ a priori from those yielding negative findings: and how those judged 'helpful' (in the sense of influencing management) differ a priori from those judged 'unhelpful'. A total of 483 patients undergoing endoscopy was sampled and a wide range of data abstracted, including 48 patient characteristics available to the gastroenterologist at the time of the decision to perform endoscopy. Sixty nine per cent of endoscopies were positive. Multivariate statistical analysis identified four variables which taken together were strongly predictive of a positive endoscopy. The resulting mathematical formula correctly predicted the outcome of 76% of endoscopies. Eighty two per cent of the endoscopies were retrospectively classified by the gastroenterologists as helpful. Six variables were strongly predictive of a helpful endoscopy. The corresponding formula correctly predicted the finding of 84% of endoscopies. Comparison of the two analyses shows that the two sets of predictions differ substantially. Thus it is important that decision tools should be based not on the crude distinction between positive and negative, but on the more useful distinction between helpful and unhelpful in influencing management.

Adolescent↗
PubMed2002

Morphometrics and the role of the phenotype in studies of the evolution of developmental mechanisms.

Developmental mechanisms are usually assumed to evolve by natural selection of the morphological traits they produce. Therefore, information on phenotypic traits is an important component of comparative studies of development. Morphometrics permits the rigorous quantitative analysis of variation in organismal size and shape, and is increasingly being used in developmental contexts. The new methods of morphometrics combine a geometric concept of shape with the procedures of multivariate statistics, and constitute a powerful and flexible set of tools for analyzing morphological variation. This paper briefly reviews these methods and provides examples of their application in studies of genetic variation and developmental modularity. The results of morphometric analyses can be readily interpreted in relation to the geometry and anatomical structure of the parts under study. Genetic studies of shape in the mouse mandible found two recurrent patterns in environmental and genetic variation from different origins, suggesting that the development system 'channels' the phenotypic expression of variation in similar ways. Moreover, by analyzing the correlations of left-right asymmetries of morphometric traits, it is possible to delimit the spatial extent of developmental modules. These methods complement the experimental approaches of developmental biology and genetics, and can be expected to be especially fruitful in combination with them.

Animals↗
PubMedDate not supplied

Metabonomic study on the biochemical profiles of a hydrocortisone-induced animal model.

This work describes the metabonomic study of a biochemical modification in vivo induced by high dose of hydrocortisone, which led to a unique pathologic condition similar to the 'kidney deficiency syndromes', an early stage of obesity and diabetes in traditional Chinese medicine. The methodology of the metabonomic approach consisted of GC/MS and multivariate statistical technique for the establishment of urine metabolic patterns of the treatment rats. In the study, 24-h urine was collected pre-dose and at days 1, 3, 7, and 10 post-dose after rats were injected with hydrocortisone at 1.5 mg/100 g. The acquired data were transferred into Matlab to be processed using principal components analysis (PCA). The results indicated that clear and consistent biochemical changes following hydrocortisone intervention under controlled conditions could be identified using chemometric analysis. The work suggests that this metabonomic approach could be used as a potentially powerful tool to investigate the biochemical changes of certain physiopathologic conditions such as metabolic syndrome, as an early diagnostic means.

Animals↗
PubMed1999

Applications of distortion-product emissions to an otological practice.

OBJECTIVES: The multiple clinical applications of distortion-product emissions (DPEs) to an otological practice are reviewed. Through an examination of studies involving thousands of infants, as well as adult ears, the relationships between measurements of DPEs and PTTs (PTTs) are examined. The cochlear physiology underlying generation of DPEs and the interpretation of these measurements are described in some detail. We study the contribution of phase measurements of DPEs to calculation of delay in cochlear traveling waves. The clinical applications of these measurements are described. The objective of this work is to demonstrate the clinical utility of DPEs through an examination of the correlation of the features of DPEs with PTTs in patients varying in age from newborn to the elderly. STUDY DESIGN METHODS: Experimental design and methodology involved careful prospective selection of large numbers of subjects in each age group, novel techniques for recording DPEs, and multivariate statistical analysis of the data. Three separate experiments encompass issues surrounding the age groups of adults, neonates, and elderly individuals. RESULTS: The results show that current techniques allow a 90% correct prediction of auditory PTTs for frequencies varying from 1,000 to 6,000 Hz, for patients of all ages. CONCLUSION: Techniques for measurement of DPEs currently represent an integral diagnostic component for an otological practice. The potential future application of measures of DPEs to diagnosis of tinnitus is described. With an extension of the technique for measuring DPEs to the phenomenon of reflectance, there may be promise of application to novel approaches to the treatment of tinnitus and the design of hearing aids.

Adolescent↗
PubMed2005

Clinical utility of fetal fibronectin for predicting preterm birth.

OBJECTIVE: To determine if fetal fibronectin can be used in a clinical setting to predict preterm birth and guide clinical management. STUDY DESIGN: We implemented a clinical protocol using the rapid fetal fibronectin test for patients presenting with symptoms of preterm labor. Adherence to the clinical pathway was at the discretion of the practitioner. Subjects who met the inclusion criteria (n = 404) were divided into 2 groups based on the fetal fibronectin result. Outcomes included time until delivery, gestational age at delivery and use of therapeutic interventions. Univariate and multivariate statistical analyses were performed. RESULTS: The 46 subjects (11.4%) with positive fetal fibronectin were more likely to deliver within 7 days, within 14 days, prior to 32 weeks' gestation and prior to 37 weeks' gestation (RR 22.0, 22.0, 12.3 and 5.1, respectively). For delivery within 7 days, the sensitivity, specificity, positive predictive value and negative predictive value were 67%, 92%, 30% and 98%, respectively. Time until delivery and gestational age at delivery were lower in women with a positive test, while the frequency of therapeutic interventions was higher (p < 0.01). CONCLUSION: A positive fetal fibronectin test is predictive of preterm birth in a clinical setting. A negative fetal fibronectin test can be used to avoid unnecessary, potentially harmful interventions.

Adult↗
PubMed1991

Identification of patients at high risk for colorectal carcinoma from biopsy studies of the apparently normal colorectal mucosa. A multivariate analysis.

A number of phenotypic abnormalities of the colorectal mucosa which appears normal have been described to be biomarkers of cancer development. To improve their sensitivity and specificity, we simultaneously determined 10 morphological and histochemical parameters in biopsies from the colonoscopically normal mucosa of the descending colon, sigmoid, and rectum. The results were analysed by multivariate statistical methods. We tested the discriminating power of proliferative, morphometric, enzyme and mucin histochemical parameters from 80 patients either at average risk (controls), with an increased risk for colorectal carcinoma (high-risk), or with a manifest carcinoma. The following parameters were investigated: number of mitotic figures per crypt, crypt length, apical, medial and basal crypt diameter, crypt surface, activity of succinate dehydrogenase (EC 1.3.99.1), activity of acid beta-galactosidase (EC 3.2.1.23), sulpho- and sialomucin contents. Univariate statistical analyses revealed that crypt length, crypt diameter and crypt surface were significantly increased in the high-risk group, the carcinoma carriers having intermediate values between average-risk and high-risk patients. In a two-group discriminant analysis, high-risk or carcinoma patients could be separated from average-risk patients with a sensitivity of 92.9% and a specificity of 100%. When the analysis was repeated for three groups (carcinoma carriers separated from high-risk patients), sensitivity and specificity were 100% for each group. We conclude that identification of patients at risk for colorectal carcinoma is possible from the normal-appearing left colonic and rectal mucosa by morphometric and cytochemical analysis of biopsies.

Aged↗
PubMed1993

Declining lymphocyte counts following cytomegalovirus (CMV) infection are associated with fatal CMV disease in bone marrow transplant patients.

A previous pilot study conducted on 12 bone marrow transplant recipients suggested that detection of cytomegalovirus (CMV) in lymphocytes was associated with a drop in lymphocyte counts and death due to CMV disease. To test the association between decreasing lymphocytes and CMV-related death, we undertook a retrospective study of 332 CMV-infected patients transplanted between 1987 and 1990. The patients were divided into three groups: I = 170 patients who survived their infection and were alive at the time of the study; II = 103 patients who died of causes other than CMV infection; and III = 59 patients who died of CMV disease. Lymphocyte counts were analyzed during a 24-day period, starting 10 days before the day of first positive CMV culture (day 0). Lymphocyte counts were significantly lower in Group III from day 0 through day +14 (p < .001 vs. group I; and p = .002 vs. group II). Multivariate statistical analysis was used to adjust for other differences between the groups that might influence lymphocyte numbers. Average lymphocyte counts in patients who died of CMV disease decreased by an average of 35% after day 0. The differences in lymphocyte counts remained independent of the effects of acute graft-vs.-host disease (GVHD), time since transplant, transplant type, and high-dose steroid treatment. In summary, these data suggest that in some patients a drop in lymphocyte counts is a consequence of CMV infection associated with fatal CMV disease. Whether this can be attributed to direct infection of lymphocytes, a defective immune response, or some other mechanism remains to be determined.

Adult↗