共查询到20条相似文献，搜索用时 31 毫秒
1.
Ordinal variables are common in many empirical investigations in the social and behavioral sciences. Researchers often apply the maximum likelihood method to fit structural equation models to ordinal data. This assumes that the observed measures have normal distributions, which is not the case when the variables are ordinal. A better approach is to use polychoric correlations and fit the models using methods such as unweighted least squares (ULS), maximum likelihood (ML), weighted least squares (WLS), or diagonally weighted least squares (DWLS). In this simulation evaluation we study the behavior of these methods in combination with polychoric correlations when the models are misspecified. We also study the effect of model size and number of categories on the parameter estimates, their standard errors, and the common chi-square measures of fit when the models are both correct and misspecified. When used routinely, these methods give consistent parameter estimates but ULS, ML, and DWLS give incorrect standard errors. Correct standard errors can be obtained for these methods by robustification using an estimate of the asymptotic covariance matrix W of the polychoric correlations. When used in this way the methods are here called RULS, RML, and RDWLS. 相似文献
2.
Data collected from questionnaires are often in ordinal scale. Unweighted least squares (ULS), diagonally weighted least squares (DWLS) and normal-theory maximum likelihood (ML) are commonly used methods to fit structural equation models. Consistency of these estimators demands no structural misspecification. In this article, we conduct a simulation study to compare the equation-by-equation polychoric instrumental variable (PIV) estimation with ULS, DWLS, and ML. Accuracy of PIV for the correctly specified model and robustness of PIV for misspecified models are investigated through a confirmatory factor analysis (CFA) model and a structural equation model with ordinal indicators. The effects of sample size and nonnormality of the underlying continuous variables are also examined. The simulation results show that PIV produces robust factor loading estimates in the CFA model and in structural equation models. PIV also produces robust path coefficient estimates in the model where valid instruments are used. However, robustness highly depends on the validity of instruments. 相似文献
3.
Previous research indicates that relative fit indices in structural equation modeling may vary across estimation methods. Sugawara and MacCallum (1993) explained that the discrepancy arises from difference in the function values for the null model with no further derivation given. In this study, we derive explicit solutions for parameters of the null model. The null model specifies the variances of the observed variables as model parameters and fixes all the covariances to be zero. Three methods of estimation are considered: the maximum likelihood (ML) method, the ordinary least squares (OLS) method, and the generalized least squares (GLS) method. Results indicate that ML and LS yield an identical estimator, which is different from GLS. Function values and associated chi‐square statistics of the null model vary across estimation methods. Consequently, relative fit indices using the null model as the reference point in computation may yield different results depending on the estimation method chosen. An illustration example is given and implications of this study are discussed. 相似文献
4.
《Structural equation modeling》2013,20(4):557-595
This simulation study demonstrates how the choice of estimation method affects indexes of fit and parameter bias for different sample sizes when nested models vary in terms of specification error and the data demonstrate different levels of kurtosis. Using a fully crossed design, data were generated for 11 conditions of peakedness, 3 conditions of misspecification, and 5 different sample sizes. Three estimation methods (maximum likelihood [ML], generalized least squares [GLS], and weighted least squares [WLS]) were compared in terms of overall fit and the discrepancy between estimated parameter values and the true parameter values used to generate the data. Consistent with earlier findings, the results show that ML compared to GLS under conditions of misspecification provides more realistic indexes of overall fit and less biased parameter values for paths that overlap with the true model. However, despite recommendations found in the literature that WLS should be used when data are not normally distributed, we find that WLS under no conditions was preferable to the 2 other estimation procedures in terms of parameter bias and fit. In fact, only for large sample sizes (N = 1,000 and 2,000) and mildly misspecified models did WLS provide estimates and fit indexes close to the ones obtained for ML and GLS. For wrongly specified models WLS tended to give unreliable estimates and over-optimistic values of fit. 相似文献
5.
Ill conditioning of covariance and weight matrices used in structural equation modeling (SEM) is a possible source of inadequate performance of SEM statistics in nonasymptotic samples. A maximum a posteriori (MAP) covariance matrix is proposed for weight matrix regularization in normal theory generalized least squares (GLS) estimation. Maximum likelihood (ML), GLS, and regularized GLS test statistics (RGLS and rGLS) are studied by simulation in a 15-variable, 3-factor model with 15 levels of sample size varying from 60 to 100,000. A key result showed that in terms of nominal rejection rates, RGLS outperformed ML at all sample sizes below 500, and GLS at most sample sizes below 500. In larger samples, their performance was equivalent. The second regularization methodology (rGLS) performed well asymptotically, but poorly in small samples. Regularization in SEM deserves further study. 相似文献
6.
Carlos G. Forero Alberto Maydeu-Olivares David Gallardo-Pujol 《Structural equation modeling》2013,20(4):625-641
Factor analysis models with ordinal indicators are often estimated using a 3-stage procedure where the last stage involves obtaining parameter estimates by least squares from the sample polychoric correlations. A simulation study involving 324 conditions (1,000 replications per condition) was performed to compare the performance of diagonally weighted least squares (DWLS) and unweighted least squares (ULS) in the procedure's third stage. Overall, both methods provided accurate and similar results. However, ULS was found to provide more accurate and less variable parameter estimates, as well as more precise standard errors and better coverage rates. Nevertheless, convergence rates for DWLS are higher. Our recommendation is therefore to use ULS, and, in the case of nonconvergence, to use DWLS, as this method might converge when ULS does not. 相似文献
7.
This article proposes 2 classes of ridge generalized least squares (GLS) procedures for structural equation modeling (SEM) with unknown population distributions. The weight matrix for the first class of ridge GLS is obtained by combining the sample fourth-order moment matrix with the identity matrix. The weight matrix for the second class is obtained by combining the sample fourth-order moment matrix with its diagonal matrix. Empirical results indicate that, with data from an unknown population distribution, parameter estimates by ridge GLS can be much more accurate than those by either GLS or normal-distribution-based maximum likelihood; and standard errors of the parameter estimates also become more accurate in predicting the empirical ones. Rescaled and adjusted statistics are proposed for overall model evaluation, and they also perform much better than the default statistic following from the GLS method. The use of the ridge GLS procedures is illustrated with a real data set. 相似文献
8.
Research in covariance structure analysis suggests that nonnormal data will invalidate chi‐square tests and produce erroneous standard errors. However, much remains unknown about the extent to and the conditions under which highly skewed and kurtotic data can affect the parameter estimates, standard errors, and fit indices. Using actual kurtotic and skewed data and varying sample sizes and estimation methods, we found that (a) normal theory maximum likelihood (ML) and generalized least squares estimators were fairly consistent and almost identical, (b) standard errors tended to underestimate the true variation of the estimators, but the problem was not very serious for large samples (n = 1,000) and conservative (99%) confidence intervals, and (c) the adjusted chi‐square tests seemed to yield acceptable results with appropriate sample sizes. 相似文献
9.
随机误差项的自相关是计量经济学模型中普遍存在的问题，本文首先分析了自相关的影响和产生原因；其次介绍了虚假自相关和真实自相关的检验方法，分析了各种方法的应用条件、注意事项和优、缺点；然后介绍了存在自相关时，应采用的模型参数估计方法-广义最小二乘法；最后，对自相关问题的检验方法进行总结，指出了它的发展方向。 相似文献
10.
Dexin Shi Christine DiStefano Heather L. McDaniel Zhehan Jiang 《Structural equation modeling》2018,25(6):924-945
This study examined the effect of model size on the chi-square test statistics obtained from ordinal factor analysis models. The performance of six robust chi-square test statistics were compared across various conditions, including number of observed variables (p), number of factors, sample size, model (mis)specification, number of categories, and threshold distribution. Results showed that the unweighted least squares (ULS) robust chi-square statistics generally outperform the diagonally weighted least squares (DWLS) robust chi-square statistics. The ULSM estimator performed the best overall. However, when fitting ordinal factor analysis models with a large number of observed variables and small sample size, the ULSM-based chi-square tests may yield empirical variances that are noticeably larger than the theoretical values and inflated Type I error rates. On the other hand, when the number of observed variables is very large, the mean- and variance-corrected chi-square test statistics (e.g., based on ULSMV and WLSMV) could produce empirical variances conspicuously smaller than the theoretical values and Type I error rates lower than the nominal level, and demonstrate lower power rates to reject misspecified models. Recommendations for applied researchers and future empirical studies involving large models are provided. 相似文献
11.
Steffen Nestler 《Structural equation modeling》2013,20(3):461-473
This article applies Bollen’s (1996) 2-stage least squares/instrumental variables (2SLS/IV) approach for estimating the parameters in an unconditional and a conditional second-order latent growth model (LGM). First, the 2SLS/IV approach for the estimation of the means and the path coefficients in a second-order LGM is derived. An empirical example is then used to show that 2SLS/IV yields estimates that are similar to maximum likelihood (ML) in the estimation of a conditional second-order LGM. Three subsequent simulation studies are then presented to show that the new approach is as accurate as ML and that it is more robust against misspecifications of the growth trajectory than ML. Together, these results suggest that 2SLS/IV should be considered as an alternative to the commonly applied ML estimator. 相似文献
12.
In the presence of omitted variables or similar validity threats, regression estimates are biased. Unbiased estimates (the causal effects) can be obtained in large samples by fitting instead the Instrumental Variables Regression (IVR) model. The IVR model can be estimated using structural equation modeling (SEM) software or using Econometric estimators such as two-stage least squares (2SLS). We describe 2SLS using SEM terminology, and report a simulation study in which we generated data according to a regression model in the presence of omitted variables and fitted (a) a regression model using ordinary least squares, (b) an IVR model using maximum likelihood (ML) as implemented in SEM software, and (c) an IVR model using 2SLS. Coverage rates of the causal effect using regression methods are always unacceptably low (often 0). When using the IVR model, accurate coverage is obtained across all conditions when N = 500. Even when the IVR model is misspecified, better coverage than regression is generally obtained. Differences between 2SLS and ML are small and favor 2SLS in small samples (N ≤ 100). 相似文献
13.
林路 《邵阳学院学报(社会科学版)》1997,(2)
统计学研究的出发点是数据集D.本文把D纳入线性回归模型M.当D有复共线性现象时,以最小二乘估计为基础的影响分析往往失效,于是,本文探讨以有编估计为基础的影响分析. 相似文献
14.
Steffen Wirth 《Teaching Statistics》2003,25(1):29-32
This article discusses the influence extreme observations can exert on linear correlation between variables. It shows that standard p‐values obtained according to ordinary least squares and median regression can be misleading. Bootstrapping can prevent underestimation of the standard error of the regression coefficient and therefore unmask the deceiving correlation. 相似文献
15.
Deborah L. Bandalos 《Structural equation modeling》2013,20(1):102-116
Robust maximum likelihood (ML) and categorical diagonally weighted least squares (cat-DWLS) estimation have both been proposed for use with categorized and nonnormally distributed data. This study compares results from the 2 methods in terms of parameter estimate and standard error bias, power, and Type I error control, with unadjusted ML and WLS estimation methods included for purposes of comparison. Conditions manipulated include model misspecification, level of asymmetry, level and categorization, sample size, and type and size of the model. Results indicate that cat-DWLS estimation method results in the least parameter estimate and standard error bias under the majority of conditions studied. Cat-DWLS parameter estimates and standard errors were generally the least affected by model misspecification of the estimation methods studied. Robust ML also performed well, yielding relatively unbiased parameter estimates and standard errors. However, both cat-DWLS and robust ML resulted in low power under conditions of high data asymmetry, small sample sizes, and mild model misspecification. For more optimal conditions, power for these estimators was adequate. 相似文献
16.
The purpose of conducting this study was to understand how neoliberal discourses manifest within the local context of a short‐term, job‐training program offered at a two‐year college in the USA. Ethnographic data were collected at the local site through interviews, observations and document analysis. We then situated these data within a global context represented by a corpus of purposively selected national and international policy texts. Focusing on three components of discourse as social action—genres, representations and identities—the data analysis illuminated three interrelated themes relating to how institutional actors translated neoliberal discourses available at the global scale into practice. The ideological consequences for learners as well as examples of counter‐hegemonic resistance are discussed. 相似文献
17.
In structural equation models, outliers could result in inaccurate parameter estimates and misleading fit statistics when using traditional methods. To robustly estimate structural equation models, iteratively reweighted least squares (IRLS; Yuan & Bentler, 2000) has been proposed, but not thoroughly examined. We explore the large-sample properties of IRLS and its effect on parameter recovery, model fit, and aberrant data identification. A parametric bootstrap technique is proposed to determine the tuning parameters of IRLS, which results in improved Type I error rates in aberrant data identification, for data sets generated from homogenous populations. Scenarios concerning (a) simulated data, (b) contaminated data, and (c) a real data set are studied. Results indicate good parameter recovery, model fit, and aberrant data identification when noisy observations are drawn from a real data set, but lackluster parameter recovery and identification of aberrant data when the noise is parametrically structured. Practical implications and further research are discussed. 相似文献
18.
A paucity of research has compared estimation methods within a measurement invariance (MI) framework and determined if research conclusions using normal-theory maximum likelihood (ML) generalizes to the robust ML (MLR) and weighted least squares means and variance adjusted (WLSMV) estimators. Using ordered categorical data, this simulation study aimed to address these queries by investigating 342 conditions. When testing for metric and scalar invariance, Δχ2 results revealed that Type I error rates varied across estimators (ML, MLR, and WLSMV) with symmetric and asymmetric data. The Δχ2 power varied substantially based on the estimator selected, type of noninvariant indicator, number of noninvariant indicators, and sample size. Although some the changes in approximate fit indexes (ΔAFI) are relatively sample size independent, researchers who use the ΔAFI with WLSMV should use caution, as these statistics do not perform well with misspecified models. As a supplemental analysis, our results evaluate and suggest cutoff values based on previous research. 相似文献
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20.
Regression techniques are used frequently to analyze the relationships between university activity variables and the needs for different categories of resources. The ordinary least squares method (LS) has the disadvantage of being very sensitive to outliers. As an alternative the least median of squares (LMS) technique is discussed, which can resist a large fraction of contaminated data. To demonstrate the advantages of LMS, the parameters of some regression equations, estimated some years ago by means of ordinary least squares, and describing the needs for nonacademic staff and operating funds in a university, will be reestimated by means of this robust regression technique. 相似文献