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1.
In predictive applications of multiple regression, interest centers on the estimation of the population coefficient of cross-validation rather than the population multiple correlation. The accuracy of 3 analytical formulas for shrinkage estimation (Ezekiel, Browne, & Darlington) and 4 empirical techniques (simple cross-validation, multicross-validation, jackknife, and bootstrap) were investigated in a Monte Carlo study. Random samples of size 20 to 200 were drawn from a pseudopopulation of actual field data. Regression models were investigated with population coefficients of determination ranging from .04 to .50 and with numbers of regressors ranging from 2 to 10. For all techniques except the Browne formula and multicross-validation, substantial statistical bias was evident when the shrunken R 2 values were used to estimate the coefficient of cross-validation. In addition, none of the techniques examined provided unbiased estimates with sample sizes smaller than 100, regardless of the number of regressors.  相似文献   

2.
Fluorescence properties of Eu^3 :Y2SiO5 have been investigated.Transitions between ^5D and ^7Fwere were studied with transmission spectra,fluorescence spectra,photoluminescence excitation(or absorption) spectra and site selective fluorescence spectra.The X-ray powder diffraction pattern of Eu^3 :Y2SiO5 shows that the crystal belong to monoclinic,and lattice‘s constants a,b,c and β arc obtaned by a simulation with the measured diffraction angles.  相似文献   

3.
We present a novel approach for dealing with optimal approximate merging of two adjacent Bezier eurves with G^2-continuity. Instead of moving the control points, we minimize the distance between the original curves and the merged curve by taking advantage of matrix representation of Bezier curve＇s discrete structure, where the approximation error is measured by L2-norm. We use geometric information about the curves to generate the merged curve, and the approximation error is smaller. We can obtain control points of the merged curve regardless of the degrees of the two original curves. We also discuss the merged curve with point constraints. Numerical examples are provided to demonstrate the effectiveness of our algorithms.  相似文献   

4.
To investigate the effect of doxorubicin(DOX) on gene expression of the myocardial sarcoplasmic reticulum (SR) Ca2+ transport proteins and the mechanism of taurine(Tau) protecting cardiac muscle cells, 9 rabbits were injected with DOX, 8 rabbits with DOX and Tau, and 9 rabbits with normal saline. Cardiac function, concentration of calcium in cardiomycocytes (Myo [Ca2+] i ), activity of SR Ca2+-ATPase (SERCA2a), level of SERCA2a mRNA and Ca2+ released channels (RYR2) mRNA were detected. The left ventricle tissues were observed by electron microscopy. The results showed that cardiac index, left ventricular systolic pressure, activity of SR Ca2+-ATPase and level of SERCA2a mRNA decreased, while Myo[Ca2+] i increased in DOX-treated rabbits. DOX could not affect the level of RYR2 mRNA. Tau intervention could alleviate the increase of left ventricular diastolic pressure, Myo[Ca2+] i and the decrease of SERCA2a mRNA induced by doxorubicin. The results suggested that downregulation of SERCA2a gene expression was an important mechanism of DOX-induced cardiomyopathy and that Tau could partially improve the heart function by reducing calcium overload and alleviating downregulation of SERCA2a mRNA.  相似文献   

5.
SO2, NO2, and PM10 are the major outdoor air pollutants in China, and most of the cities in China have regulatory monitoring sites for these three air pollutants. In this study, we developed a land use regression （LUR） model using regulatory monitoring data to predict the spatial distribution of air pollutant concentrations in Jinan, China. Traffic, land use and census data, and meteorological and physical conditions were included as candidate independent variables, and were tabulated for buffers of varying radii. SO2, NO2, and PM10 concentrations were most highly correlated with the area of industrial land within a buffer of 0.5 km （R2=0.34）, the distance from an expressway （R2=0.45）, and the area of residential land within a buffer of 1.5 km （R2=0.25）, respectively. Three multiple linear regression （MLR） equations were established based on the most significant variables （p〈0.05） for SO2, NO2, and PM10, and R2 values obtained were 0.617, 0.640, and 0.600, respectively. An LUR model can be applied to an area with complex terrain. The buffer radii of independent variables for SO2, NO2, and PM10 were chosen to be 0.5, 2, and 1.5 kin, respectively based on univariate models. Intercepts of MLR equations can reflect the background concentrations in a certain area, but in this study the intercept values seemed to be higher than background concentrations. Most of the cities in China have a network of regulatory monitoring sites. However, the number of sites has been limited by the level of financial support available. The results of this study could be helpful in promoting the application of LUR models for monitoring pollutants in Chinese cities.  相似文献   

6.
The purpose of this research is to analyze the relationship between individual, institutional and demographic characteristics on one hand and the research productivity of agriculture faculty members on the other. The statistical population of the research comprises 280 academic staff in agricultural faculties all over Tehran Province. The data regarding research productivity and demographic characteristics were extracted from the faculty members’ profiles. Questionnaires were utilized to collect information concerning individual and institutional variables. The reliably of the questionnaire was calculated to be between 0.74 and 0.97 using the Cronbach’s Alpha. The regression analysis revealed that from among demographic characteristics two variables, namely, academic rank and age ( \textR\textAD 2 {\text{R}}_{\text{AD}}^{ 2}  = 0.265), among individual characteristics, three variables, namely, working habits, creativity as well as autonomy and commitment ( \textR\textAD 2 {\text{R}}_{\text{AD}}^{ 2}  = 0.097), and among institutional characteristics four variables namely, network of communication with colleagues, resources of facilities, corporate management and clear research objectives ( \textR\textAD 2 {\text{R}}_{\text{AD}}^{ 2}  = 0.151) were significant predictors for agricultural faculty members’ research productivity.  相似文献   

7.
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8.
Objective: In addition to pH regulation, Na+/H+ exchange (NHE) has been shown to facilitate cell growth and proliferation. However, the effects of long-term inhibition of Na+/H+ exchange on cardiac structural and functional remodeling post myocardial infarction (MI) are still controversial. The present study was therefore carried out to further investigate the effects of long-term treatment with cariporide, a specific inhibitor of NHE-1, on cardiac remodeling after MI in rats; Methods: Male Wistar rats that underwent coronary ligation were randomly selected for cariporide treatment starting 6 h after induction of MI or no treatment. Treatment was continued up to 6 weeks post MI, after which, the arterial, venous and left ventricular catheters were chronically implanted. Twenty-four h later, after hemodynamic signals were recorded in conscious rats, they were sacrificed and hearts were taken out for morphological examinations; Results: Cariporide treatment decreased the heart weight and heart weight to body weight ratio (bothP<0.05), decreased left ventricular end-diastolic pressure (P<0.001), improved myocardial contractility (dP/dt max) (P<0.05) and tended to increase the survival of treated rats compared to that of untreated infarct rats; Conclusion: The results of the present study indicate that the long-term inhibition of NHE with cariporide can attenuate cardiac structural remodeling and improve left ventricular dysfunction in infarcted rats, and suggest that Na+/H+ exchange inhibition could be an effective therapeutic strategy for myocardial infarction-induced heart failure.  相似文献   

9.
Approximations to the distributions of goodness-of-fit indexes in structural equation modeling are derived with the assumption of multivariate normality and slight misspecification of models. The fit indexes considered in this article are Joreskog and Sorbom's goodness-of-fit index (GFI) and the adjusted GFI, McDonald's absolute GFI, Steiger and Lind's root mean squared error of approximation, Steiger's Γ1 and Γ2, Bentler and Bonett's normed fit index, Bollen's incremental fit index and ρ1, Tucker and Lewis's index ρ2, and Bentler's fit index (McDonald and Marsh's relative noncentrality index). An approximation to the asymptotic covariance matrix for the fit indexes is derived by using the delta method. Furthermore, approximations to the densities of the fit indexes are obtained from the transformations of the asymptotically noncentral chi-square distributed variable. A simulation is carried out to confirm the accuracy of the approximations.  相似文献   

10.
本文在一定条件下研究Briot—Bouquet型微分方程的解析解及其在λ——螺形函数中的应用。  相似文献   

11.
LetH n be the set of real algebraic polynomials of degreen, whose zeros all lie in the interval [−1,1]. The well known Turán type inequalities tell us that forf(x)∈H n , it holds ‖f′‖≥C√n‖f‖. This note deals with the weighted Turán type inequalities with the weights having inner singularities underL p norm for 0<p≤∞. Our results essentially extend the result of Wang and Zhou (2002), and the method used in this paper is simpler and more direct than that of Wang and Zhou (2002). The results and methods have their own values in approximation theory and computation.  相似文献   

12.
Let Bnp={x ∈ Rn‖|x ‖p≤l} be the unit ball ofp norm in the n-dimensional normed space p. The formula for the volume of Bnp was obtained and its asymptotic properties were found out as n→∞and p→∞.  相似文献   

13.
Genetic influences on reading are investigated in a sample of 285, 13 year old twins. Using a multiple regression procedure, the heritability of disability (h g 2 ) for Reading Recognition was found to be non-significant. However the h g 2 for spelling disability was found to be 0.58 (P<0.05), after controlling for individual differences in IQ. The twins in this study were an unselected sample from the general population. Therefore it was possible to estimate h g 2 for differing degrees of severity of disability. These analyses showed that for spelling but not for Reading Recognition or Reading Composite, there were substantial genetic contributions to all levels of disability. For indices of Orthographic Coding there were no significant values of h g 2 . In contrast measures of Phonological Coding and Homophone Recognition have consistently high values of h g 2 . More detailed analyses suggested that there were possibly two independent aspects of phonological ability, each influenced by genetic factors.  相似文献   

14.
Abstract

Scoring multipie-choice questions according to the simple scoring systems S1 = R, where R is the number of correct answers, produces an upward bias in scores of poorer students as a result of guessing. The scoring formula conventionally used to adjust for guessing is S2 R-W/(n-1), where W is the number of wrong answers and nis the number of choices per question. However, S2 is based on the unrealistic assumption that on each question the student either knows the correct answer or guesses randomly. On the basis of a more realistic assumption an alternative scoring formula is derived, S4 = [nR + (n-1)Q - Q2/R]/2(n-1), where Q is the number of questions. Compared to S4, the conventional formula (S2) has a downward bias for Q/n < R < Q and the simple formula (S1) has a downward bias for Q/(n-2)<R<Q in addition to its upward bias for R<Q/(n-2).  相似文献   

15.
Date pits for feed preparation or oil extraction are soaked in water to soften before milling or extrusion. Knowledge of water absorption by the date pits helps in better managing the soaking duration. In this research, the process of water absorption by date pits was modeled and analyzed using Fick's second law of diffusion, finite element approach, and Peleg model. The moisture content of the pits reached to its saturation level of 41.5% (wet basis) after 10 d. The estimated coefficient of diffusion was 9.89×10-12 m2/s. The finite element model with a proposed ellipsoid geometry for a single date pit and the analytical model fitted better to the experimental data with R2 of 0.98. The former model slightly overestimated the moisture content of the pits during the initial stages of the soaking and the latter model generally underestimated this variable through the entire stages of soaking process.  相似文献   

16.
Fatty acids and derivatives (FADs) are resources for natural antimicrobials. In order to screen for additional potent antimicrobial agents, the antimicrobial activities of FADs against Staphylococcus aureus were examined using a microplate assay. Monoglycerides of fatty acids were the most potent class of fatty acids, among which monotridecanoin possessed the most potent antimicrobial activity. The conventional quantitative structure-activity relationship (QSAR) and comparative molecular field analysis (CoMFA) were performed to establish two statistically reliable models (conventional QSAR: R 2=0.942, Q 2 LOO=0.910; CoMFA: R 2=0.979, Q 2=0.588, respectively). Improved forecasting can be achieved by the combination of these two models that provide a good insight into the structure-activity relationships of the FADs and that may be useful to design new FADs as antimicrobial agents.  相似文献   

17.
In social science research, a common topic in multiple regression analysis is to compare the squared multiple correlation coefficients in different populations. Existing methods based on asymptotic theories (Olkin & Finn, 1995) and bootstrapping (Chan, 2009) are available but these can only handle a 2-group comparison. Another method based on structural equation modeling (SEM) has been proposed recently. However, this method has three disadvantages. First, it requires the user to explicitly specify the sample R2 as a function in terms of the basic SEM model parameters, which is sometimes troublesome and error prone. Second, it requires the specification of nonlinear constraints, which is not available in some popular SEM software programs. Third, it is for a 2-group comparison primarily. In this article, a 2-stage SEM method is proposed as an alternative. Unlike all other existing methods, the proposed method is simple to use, and it does not require any specific programming features such as the specification of nonlinear constraints. More important, the method allows a simultaneous comparison of 3 or more groups. A real example is given to illustrate the proposed method using EQS, a popular SEM software program.  相似文献   

18.
This study examined the performance of 4 correlation-based fit indexes (marginal and conditional pseudo R 2s; average and conditional concordance correlations) in detecting misspecification in mean structures in growth curve models. Their performance was also compared to that of 4 traditional SEM fit indexes. We found that the marginal pseudo R 2 and average concordance correlation were able to detect misspecification in the marginal mean structure (average change trajectory). The conditional pseudo R 2 and concordance correlation could detect misspecification when it occurred in the conditional mean structure (individual change trajectory) or in both mean structures. Compared to the SEM fit indexes, the correlation-based fit indexes were more robust to sample size but were less robust to data properties such as magnitude of population mean and measurement error. Theoretical and practical implications of the results and directions for future research are discussed.  相似文献   

19.
Selecting a subset of predictors from a pool of potential predictors continues to be a common problem encountered by applied researchers in education. Because of several limitations associated with stepwise variable selection procedures, the examination of all possible regression solutions has been recommended. The authors evaluated the use of Mallow's Cp and Wherry's adjusted R 2 statistics to select a final model from a pool of model solutions. Neither the Cp nor the adjusted R 2 statistic correctly identified the underlying regression model any better and was generally worse than the stepwise selection method, which itself was poor. Using any of the model selection procedures studied here resulted in biased estimates of the authentic regression coefficients and underestimation of their standard errors. The use of theory and professional judgment is recommended for the selection of variables in a prediction equation.  相似文献   

20.
In developed countries, healthy retirees can fulfill their life, but may fear growing old. Yet, there is little empirical data on the relationship between this fear and life satisfaction. This cross-sectional, correlational survey study tested whether a new, summated measure of Fears About Growing Old (FAGO)—derived from exemplifications of Laslett, who posited the theory of the Third Age—significantly predicted life satisfaction and retirement satisfaction after adjusting for significant social participation covariates. A total of 190 Canadian retirees at three senior centers in Ontario, Canada, completed surveys. A pilot study established the reliability and validity of the scales, including the FAGO, used to assess the independent variable. In a regression analysis, fear (R 2 change = .06) was found to be a statistically significant predictor of life satisfaction when controlling for five covariates (current activity, circumstance and pursuing own interest as two reasons for retirement, postretirement work, and perceived social support); overall R 2 = .26. For retirement satisfaction, fear significantly explained variance in the outcome (R 2 change  = .04) while controlling for two significant covariates (current activity and perceived social support); overall R 2 = .14. A work by gender interaction on satisfaction was not found. Other than fear about loss of mobility, men rated loss of partner very high; women rated mortal disease very high. The lowest fear was loss of retirement income for men and loss of earning-power for women. Canada's poverty preventive programs successfully supported senior postretirement life. The FAGO was useful to find senior needs.  相似文献   

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