PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Linear Models”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 1,243 records · Page 69Linked to original sources
PubMed2005

Alveolar ridge augmentation: a comparative longitudinal study between calvaria and iliac crest bone grafrs.

Insertion of endosseous implants is often difficult because of lack of supporting bone. In the case of severe atrophy of the jaws, a large volume of autogenous bone can be harvested from the iliac crest and calvaria. Both grafts undergo partial resorption with time, but the rate of bone loss has not been fully elucidated. The aim of this study was to evaluate the alveolar bone height gain (ABHG) obtained with iliac crest and calvaria bone grafts. Twenty-five patients had mandibular bone grafts, 32 had maxillary bone grafts, and 11 had both mandibular and maxillary bone grafts. Measures were made on preoperative, postoperative, and follow-up radiographs. A general linear model was used to evaluate the rate of ABHG plotted against months elapsed from the time of the operation to the time of follow-up. General linear model output showed a statistically significant effect for only the type of donor bone graft (P =.004), with a better ABHG for calvaria. The iliac crest bone grafts lost most of the ABHG in the first 6 months, whereas calvaria bone grafts lost ABHG over a greater interval of time. The type of bone graft is the strongest predictor of ABHG, and calvaria bone graft had a higher stability than did iliac bone graft. However, the gap in ABHG between the 2 grafts tended to decrease over time.

Adult↗
PubMed1994

Estimation of chronic phase duration in Ph-positive chronic myelocytic leukemia treated with busulfan: statistical analysis on Japanese patients.

Chronic phase duration was analyzed in 148 Japanese patients with Ph-positive chronic myelocytic leukemia (CML) treated only with busulfan, and multivariate proportional hazard models were constructed to infer the prognosis of a given patient, and to evaluate the prognostic importance of the clinical findings. To make an accurate estimation of an individual patient's prognosis, we introduced a piecewise linear model for describing a hazard function in each prognostic variable. Of the 11 prognostic variables initially analyzed, the absolute count of peripheral basophils was revealed as the most important prognostic factor. A high basophil count was clearly a factor in cases with poor prognosis. The statistical model selection based on the criteria of model approximation finally suggested a model with three covariates; absolute count of peripheral basophils, platelet count, and presence or absence of additional chromosome abnormalities superimposed on the translocation of 9;22. By analyses based on the above model, we estimated that the median of the chronic phase duration for the patients with poor and good prognosis was 12 and 75 months, respectively. The piecewise linear model was well suited for an accurate estimation of an individual patient's prognosis. Thus, the model constructed here would become a reliable control to evaluate investigational approaches, such as hydroxyurea, interferons, and/or bone marrow transplantation.

Adolescent↗
PubMed2006

An accurate and interpretable model for siRNA efficacy prediction.

BACKGROUND: The use of exogenous small interfering RNAs (siRNAs) for gene silencing has quickly become a widespread molecular tool providing a powerful means for gene functional study and new drug target identification. Although considerable progress has been made recently in understanding how the RNAi pathway mediates gene silencing, the design of potent siRNAs remains challenging. RESULTS: We propose a simple linear model combining basic features of siRNA sequences for siRNA efficacy prediction. Trained and tested on a large dataset of siRNA sequences made recently available, it performs as well as more complex state-of-the-art models in terms of potency prediction accuracy, with the advantage of being directly interpretable. The analysis of this linear model allows us to detect and quantify the effect of nucleotide preferences at particular positions, including previously known and new observations. We also detect and quantify a strong propensity of potent siRNAs to contain short asymmetric motifs in their sequence, and show that, surprisingly, these motifs alone contain at least as much relevant information for potency prediction as the nucleotide preferences for particular positions. CONCLUSION: The model proposed for prediction of siRNA potency is as accurate as a state-of-the-art nonlinear model and is easily interpretable in terms of biological features. It is freely available on the web at http://cbio.ensmp.fr/dsir.

Algorithms↗
PubMed1996

Cancer mortality among Techa River residents and their offspring.

This paper analyzes the data on leukemia and solid cancers of all types among 28,000 people exposed due to discharges of radioactive waste into the Techa River in the South Urals. Cancer mortality rates for the 33-y period since the beginning of the exposure have been estimated. In addition, the paper discusses malignancy cases among the first generation offspring of the exposed people. In comparison with matched control groups, an increased incidence of malignant neoplasms was observed among the exposed population. The leukemia risk, estimated on the basis of the linear model of absolute risk, was 0.85 per 10,000 person-y Gy of the dose accumulated in red bone marrow. Solid cancer risk (except osteosarcoma), estimated using linear model of relative risk, was 0.65 per Gy of dose accumulated in soft tissues. No increase in cancer mortality has been documented for the offspring of the exposed individuals.

Adolescent↗
PubMed2006

MDCT angiography of the spinal vasculature and the artery of Adamkiewicz.

OBJECTIVE: The purpose of our study was to prospectively assess 40-MDCT technology in combination with adapted brain reconstruction algorithms to visualize the spinal vasculature, in particular the artery of Adamkiewicz and its anatomic variants. SUBJECTS AND METHODS: One hundred patients underwent contrast-enhanced MDCT of the thoracolumbar junction with collimation of 40 x 0.625 mm. The adapted brain algorithm reconstructed the spinal canal with a field of view of 90 mm at 0.6-mm slice thickness. Curved multiplanar reformations identified the artery of Adamkiewicz as a continuous vascular tract extending from the aortic orifices of the intercostal or lumbar arteries via the anterior radiculomedullary artery to the anterior spinal artery. Segment of origin and length were noted. Diameter and contrast-to-noise ratio (CNR) were evaluated along the posterior branch, the radiculomedullary artery, the artery of Adamkiewicz, and the anterior spinal artery. Univariate general linear model analysis with Bonferroni post hoc corrections evaluated whether laterality, segment of origin, and length of the artery of Adamkiewicz showed a sex-specific propensity. Multivariate general linear model analysis assessed whether spinal vascular diameters and intraluminal CNR showed correlations with sex, laterality, and segment of origin. Finally, the luminal diameters of the feeding posterior branches were statistically compared with those of the ipsilateral and contralateral adjacent posterior branches. RESULTS: Successful depiction of the artery of Adamkiewicz was achieved in all patients; longitudinally the artery measured 40.1 +/- 13.51 mm. In 63% of patients it originated from the left side of the body, and in 74% it originated from the level of the 10th-12th thoracic vertebrae. Duplications were found in 5% of patients. Segmental distribution, laterality, and length did not show significant sex-specific differences (p > 0.05). The vascular diameter and luminal contrast did not show significant differences caused by sex, laterality, or segment of origin (p > 0.05). The diameter of the posterior branches (2.8 +/- 0.71 mm) arising in the segments of origin showed a significantly wider lumen than any of the other posterior branches (contralateral, 1.9 +/- 0.32 mm; upper ipsilateral, 2.0 +/- 0.47 mm; lower ipsilateral, 1.9 +/- 0.39 mm) (p < 0.0001). CONCLUSION: Contrast-enhanced 40-MDCT technology, in combination with an adapted brain reconstruction algorithm, can depict the artery of Adamkiewicz and its anatomic variants.

Adult↗
PubMedDate not supplied

An integrated approach for the computer-assisted treatment of diabetic patients on insulin.

A prototype computer system has been developed to provide advice on the day-to-day adjustment of carbohydrate intake and insulin regimen in the insulin-dependent diabetic patient. The system also produces a 24-h simulation of the patient's blood glucose profile based on these adjustments. Advice is generated by a qualitative knowledge-based system which suggests what the next step in improving glycaemic control might be for a given patient, e.g. 'decrease morning short-acting insulin by 2 units'. The quantitative simulator module contains two different mathematical models. The first is a non-linear model in differential equation form which consists of a one-compartment glucose model linked to a model with free and bound insulin compartments. This physiological model is solved by a general-purpose simulation engine. The second is a linear systems model which uses a transfer function to describe the insulin input/blood glucose response relationship for individual diabetic patients. Results of a preliminary medical validation are presented.

Blood Glucose↗
PubMedDate not supplied

[Analysis of experiments on kinetics of recycling of asialoglycoprotein receptors on the basis of a mathematical model].

By means of a linear model of receptor-mediated endocytosis experiments on the kinetics of binding and internalisation of asialoglycoproteins were analysed, as well as the dependence of ligand binding on the cells of human hepatoma HepG2 on asialoglycoprotein concentration in the medium described earlier. The kinetic constants of the process were determined. The analysis presented discards the hypothesis advanced by Schwartz et al. that at high concentrations of asialoglycoproteins in the medium the recycling of receptors of the tumor cells of HepG2 is inhibited.

Asialoglycoprotein Receptor↗
PubMedDate not supplied

Prediction of the left ventricular ejection fraction response to doxorubicin using a multiple linear regression model.

The aim of this study was to develop a model for predicting clinically significant deterioration in the left ventricular ejection fraction due to chronic doxorubicin administration. Twenty-six patients were monitored during their courses of doxorubicin chemotherapy with serial gated equilibrium radionuclide angiography. Multiple linear regression analysis was used to derived the best combination of clinical and radionuclide angiographic predictors of resting left ventricular ejection fraction at any point during the course of chemotherapy. The final model consisted of five variables: left ventricular ejection fraction at the previous monitoring point; cumulative dose of doxorubicin achieved at the previous monitoring point; increment in dose from the previous monitoring point; age of the patient; and time to peak left ventricular emptying at the previous monitoring point. The cumulative dose, the ejection fraction at the previous monitoring point and the final model, respectively, explained 11%, 33% and 53% of the variability in ejection fraction determinations during the 26 patient courses. The final model also forecast a potentially very low resting left ventricular ejection fraction (less than 35%) at the cumulative doses of doxorubicin which provoked serious clinical cardiotoxicity in two patients. A multivariate model is a useful aid in timing discontinuation of doxorubicin prior to the development of a clinically significant deterioration in left ventricular ejection fraction.

Computer Simulation↗
PubMed2004

A measurement error model with a Poisson distributed surrogate.

We study a linear model in which one of the covariates is measured with error. The surrogate for this covariate is the event count in unit time. We model the event count by a Poisson distribution, the rate of which is the unobserved true covariate. We show that ignoring the measurement error leads to inconsistent estimators of the regression coefficients and propose a set of unbiased estimating equations to correct the bias. The method is computationally simple and does not require using supplemental data as is often the case in other measurement error analyses. No distributional assumption is made for the unobserved covariate. The proposed method is illustrated with an example from the Wisconsin Sleep Cohort Study.

Bias↗
PubMed2005

Serum creatinine and cholesterol levels of testicular cancer patients in long-term follow up.

PURPOSE: Most patients with advanced testicular cancer can be cured with cisplatin-based chemotherapy. Therefore, the long-term effects of the treatment are clinically important. In the present study, we evaluated the serum creatinine and cholesterol levels of long-term survivors of testicular cancer. METHODS: Serum creatinine and cholesterol levels were determined in 23 testicular cancer patients who had received cisplatin-based chemotherapy more than 5 years earlier. They were compared with a control group of 16 patients who did not receive chemotherapy. In addition, follow-up data of beyond 10 years after the initial treatment was obtained from 17 patients. We also analysed the trends of both serum creatinine and cholesterol determinations over 10 or more years using a generalized linear model. RESULTS: There was no significant difference in the serum creatinine and cholesterol levels 5 years after the treatment between the chemotherapy and control groups. Analysis using a generalized linear model showed a significant trend toward an increase in serum creatinine in patients who had developed renal dysfunction during chemotherapy (P = 0.0024). The elevation of the serum creatinine level was mainly observed during the first 5 years. In addition, a significant trend toward an increase in serum cholesterol was revealed in both the chemotherapy and control groups. CONCLUSION: Patients who have developed renal dysfunction during chemotherapy may be at risk of gradually increasing serum creatinine levels even after it has become normal. Although further analysis is needed, we recommend long-term follow up in the survivors of metastatic testicular cancer patients treated with cisplatin-based chemotherapy.

Adult↗
PubMed2003

On the sensitivity of wall stresses in diseased arteries to variable material properties.

Accurate estimates of stress in an atherosclerotic lesion require knowledge of the material properties of its components (e.g., normal wall, fibrous plaque, calcified regions, lipid pools) that can only be approximated. This leads to considerable uncertainty in these computational predictions. A study was conducted to test the sensitivity of predicted levels of stress and strain to the parameter values of plaque used in finite element analysis. Results show that the stresses within the arterial wall, fibrous plaque, calcified plaque, and lipid pool have low sensitivities for variation in the elastic modulus. Even a +/- 50% variation in elastic modulus leads to less than a 10% change in stress at the site of rupture. Sensitivity to variations in elastic modulus is comparable between isotropic nonlinear, isotropic nonlinear with residual strains, and transversely isotropic linear models. Therefore, stress analysis may be used with confidence that uncertainty in the material properties generates relatively small errors in the prediction of wall stresses. Either isotropic nonlinear or anisotropic linear models provide useful estimates, however the predictions in regions of stress concentration (e.g., the site of rupture) are somewhat more sensitive to the specific model used, increasing by up to 30% from the isotropic nonlinear to orthotropic model in the present example. Changes resulting from the introduction of residual stresses are much smaller.

Anisotropy↗
PubMed1995

Randomization model methods for evaluating treatment efficacy in multicenter clinical trials.

This paper studies randomization model methods for analyzing data from a multicenter study comparing the effectiveness of two treatments. The Mantel-Haenszel mean score statistic, which can be used for continuous or ordered categorical response variables, is shown to be a useful nonparametric alternative to standard linear model methods for testing the significance of the average treatment difference. In an extensive simulation study, the mean score test performs nearly as well as the optimal linear model methods when the normal-theory assumptions are satisfied. A related estimator of the average treatment difference is also studied. This estimator, which is a weighted average of the center-specific mean differences, is analogous to the commonly used Mantel-Haenszel estimator of the average odds ratio in stratified 2 x 2 contingency tables. The proposed estimator is equivalent to the fixed-effects analysis of variance estimator from the main effects model, and valid estimation of its variance is feasible under very general assumptions.

Aged↗
PubMed1990

Genetic and environmental factors in adoptee antisocial personality.

In a sample of 286 adult male adoptees 44 met criteria for antisocial personality (ASP). Two types of biologic parent background were associated with increased incidence of ASP in offspring: those with alcohol problem and those with a criminal conviction or adjudged delinquency. ASP adoptees were also significantly more likely to be alcoholic. Log linear modeling showed that alcohol problems in a biologic parent predicted increased alcohol abuse in the adoptee and that criminality/delinquency in a biologic parent predicted adult adoptee ASP. In the log-linear model two environmental factors significantly increased adoptee ASP: (1) placement in an adoptive home where there was an alcohol problem or antisocial behavior; and (2) placement in a lower socioeconomic home when the adoptee came from a background of criminality/delinquency in a biologic parent. When the adoptee did not have this biologic background socioeconomic level appeared to have little effect on ASP incidence. The results suggest the importance of genetic-environmental interaction in the genesis of adult ASP disorder.

Adoption↗
PubMed1999

Reliability of an ordinal rating system for assessing the amount of mud and feces (tag) on cattle hides at slaughter.

A study was conducted to provide a quantitative description of the amount of tag (mud, soil, and bedding) adhered to the hides of feedlot beef cattle and to appraise the statistical reliability of a subjective rating system for assessing this trait. Initially, a single rater obtained baseline data by assessing 2,417 cattle for 1 month at an Ontario beef processing plant. Analysis revealed that there was a strong tendency for animals within sale-lots to have a similar total tag score (intralot correlation = 0.42). Baseline data were summarized by fitting a linear model describing an individual's total tag score as the sum of their lot mean tag score (LMTS) plus an amount representing normal variation within the lot. LMTSs predicted by the linear model were adequately described by a beta distribution with parameters nu = 3.12 and omega = 5.82 scaled to fit on the 0-to-9 interval. Five raters, trained in use of the tag scoring system, made 1,334 tag score observations in a commercial abattoir, allowing reliability to be assessed at the individual level and at the lot level. High values for reliability were obtained for individual total tag score (0.84) and lot total tag score (0.83); these values suggest that the tag scoring system could be used in the marketing and slaughter of Ontario beef cattle to improve the cleanliness of animals presented for slaughter in an effort to control the entry of microbial contamination into abattoirs. Implications for the use of the tag scoring system in research are discussed.

Abattoirs↗
PubMed1991

An ellipsoidal representation of human hand anthropometry.

The goal of this study was to collect anthropometric data that describe the geometry of the surface of the hand and to model this anthropometry as a function of gross external hand measurements. The depth and breadth of each segment of the hand were measured at points that were spaced at approximately equal distances between the joints of the hand. Linear models using hand breadth as the independent variable explained from 12% to 47% of the variation in segment breadths and from 6% to 74% in segment depths. Ellipsoids are used in biomechanical models as an efficient mathematical description of the shape of kinematic segments for use in the determination of contact with other objects. Therefore the primary objectives of this study were to approximate the semiaxis dimensions for these hand segment contact bodies using a linear model of the gross anthropometry and to evaluate the accuracy with which ellipsoids describe the geometry of the hand segments. Graphical comparisons showed that differences between the ellipsoidal approximations and the breadth and depth measurements were largest near the joints. Data collected in this study could be used to create a set of overlapping ellipsoids that would provide a more accurate representation of hand geometry, and this representation could be adapted to biomechanical models that use ellipsoids to define segment geometry.

Adult↗
PubMed1994

Phylogenetic inference under the pure drift model.

When pairwise genetic distances are used for phylogenetic reconstruction, it is usually assumed that the genetic distance between two taxa contains information about the time after the two taxa diverged. As a result, upon an appropriate transformation if necessary, the distance usually can be fitted to a linear model such that it is expressed as the sum of lengths of all branches that connect the two taxa in a given phylogeny. This kind of distance is referred to as "additive distance." For a phylogenetic tree exclusively driven by random genetic drift, genetic distances related to coancestry coefficients (theta XY) between any two taxa are more suitable. However, these distances are fundamentally different from the additive distance in that coancestry does not contain any information about the time after two taxa split from a common ancestral population; instead, it reflects the time before the two taxa diverged. In other words, the magnitude of theta XY provides information about how long the two taxa share the same evolutionary pathways. The fundamental difference between the two kinds of distances has led to a different algorithm of evaluating phylogenetic trees when theta XY and related distance measures are used. Here we present the new algorithm using the ordinary-least-squares approach but fitting to a different linear model. This treatment allows genetic variation within a taxon to be included in the model. Monte Carlo simulation for a rooted phylogeny of four taxa has verified the efficacy and consistency of the new method. Application of the method to human population was demonstrated.

Animals↗
PubMed2006

Is high job strain associated with hypertension genesis?

BACKGROUND: The aim of this analysis was to test, in a large sample of normotensive subjects, the short-term influence of job strain on the onset of hypertension. METHODS: According to the questionnaire of Karasek et al, job strain was divided into four modalities: (high strain, low strain, passive, and active) based on job demand (eg, the need to work hard and quickly) and job latitude (eg, control over skill use, time allocation, and organizational decisions) scores. High strain (HS) was defined by a high demand and a low job decision latitude. Individual data obtained in 926 (age 41 +/- 6 years) healthy normotensive or newly diagnosed hypertensive subjects were analyzed. Subjects participated in two prospective work site surveys designed to assess the influence of job strain on hypertension development. Relationships between job strain modalities and work site blood pressure (BP) levels were assessed using a general linear model. A complementary analysis using the the Pearson Phi coefficient (Z analysis) was implemented to explore nonlinear or scattered relationships between job strain and onset of hypertension. RESULTS: Systolic BP (SBP) was linearly related significantly to BMI and alcohol consumption, whereas diastolic BP (DBP) was related to age. The linear model did not find any relationship between SBP or DBP and job strain modalities. Using the Z analysis, development of systolic hypertension (SBP >140 mm Hg) was significantly associated with high job strain (P < .001). CONCLUSIONS: Our results suggest that there is no global relationship between job strain and BP levels. However our methodology revealed a significant association between job strain and work site BP in a predominantly male subgroup of newly diagnosed hypertensive subjects exposed to high job strain.

Adult↗