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1.
The asymptotically distribution free (ADF) method is often used to estimate parameters or test models without a normal distribution assumption on variables, both in covariance structure analysis and in correlation structure analysis. However, little has been done to study the differences in behaviors of the ADF method in covariance versus correlation structure analysis. The behaviors of 3 test statistics frequently used to evaluate structural equation models with nonnormally distributed variables, χ2 test TAGLS and its small-sample variants TYB and TF(AGLS) were compared. Results showed that the ADF method in correlation structure analysis with test statistic TAGLS performs much better at small sample sizes than the corresponding test for covariance structures. In contrast, test statistics TYB and TF(AGLS) under the same conditions generally perform better with covariance structures than with correlation structures. It is proposed that excessively large and variable condition numbers of weight matrices are a cause of poor behavior of ADF test statistics in small samples, and results showed that these condition numbers are systematically increased with substantial increase in variance as sample size decreases. Implications for research and practice are discussed.  相似文献   

2.
In this study we examined procedures for assessing model-data fit of item response theory (IRT) models for mixed format data. The model fit indices used in this study include PARSCALE's G2 , Orlando and Thissen's S − X2 and S − G2 , and Stone's χ2* and G2* . To investigate the relative performance of the fit statistics at the item level, we conducted two simulation studies: Type I error and power studies. We evaluated the performance of the item fit indices for various conditions of test length, sample size, and IRT models. Among the competing measures, the summed score-based indices S − X2 and S − G2 were found to be the sensible and efficient choice for assessing model fit for mixed format data. These indices performed well, particularly with short tests. The pseudo-observed score indices, χ2* and G2* , showed inflated Type I error rates in some simulation conditions. Consistent with the findings of current literature, the PARSCALE's G2 index was rarely useful, although it provided reasonable results for long tests.  相似文献   

3.
Marsh and Balla (1986) and Marsh, Balla, and McDonald (1988) proposed an index of fit called χ2I2, but McDonald and Marsh (1990) subsequently demonstrated that the index is biased and recommended that it not be used. Bollen (1989) independently proposed Δ2 which is the same as χ2I2 (hereafter referred to as χ2I2‐Δ2), indicating that it adjusts for sample size and degrees of freedom (df). Gerbing and Anderson (1992), apparently based on the assumption that the χ2I2‐Δ2 index is unbiased and appropriately corrects for df (penalizes a lack of parsimony), recommended its use, and the index is routinely presented by major computer programs (e.g., EQS and LISREL 8). However, a more critical evaluation of the χ2I2‐Δ2 index reveals that: (a) it is systematically biased (i.e., its value varies systematically with N) although the size of the bias may be small; (b) the adjustment for df is inappropriate in that it penalizes model parsimony instead of model complexity; and (c) the inappropriate penalty for model parsimony is larger for small N. Because of these undesirable properties, the χ2I2‐Δ2 index is not recommended for routine use.  相似文献   

4.
A major issue in the utilization of covariance structure analysis is model fit evaluation. Recent years have witnessed increasing interest in various test statistics and so-called fit indexes, most of which are actually based on or closely related to F 0, a measure of model fit in the population. This study aims to provide a systematic investigation about the performance of 4 available estimators of F 0. [Fcirc]01 is the conventional estimator and is based on noncentral chi-square approximation. [Fcirc]02 is newly proposed and does not assume noncentral chi-square approximation. [Fcirc]03 and [Fcirc]04 are variations of [Fcirc]02. A Monte Carlo simulation study is conducted to examine how these four estimators of F 0 perform across varying model misspecifications, data distributions, model sizes, and sample sizes. The results show that under normality all 4 quantities estimate F 0 equally well, and under nonnormality [Fcirc]02, [Fcirc]03, and [Fcirc]04 outperform [Fcirc]01. Issues related to these findings are discussed.  相似文献   

5.
Consider the positive d-dimensional lattice d (d≥2) with partial ordering ≤, let {XK; K ∈ d } be i.i.d. random vari- ables taking values in a real separable Hilbert space (H, ||·||) with mean zero and covariance operator ∑, and set partial sums SN =∑K≤NXK, K , N ∈ d . Under some moment conditions, we obtain the precise asymptotics of a kind of weighted infinite series for partial sums SN as ε 0 by using the truncation and approximation methods. The results are related to the convergence rates of the law of the logarithm in Hilbert space, and they also extend the results of (Gut and Spǎtaru, 2003).  相似文献   

6.
In this paper we study the scaling behavior of nucleotide cluster in 11 chromosomes of Encephalitozoon cuniculi Genome. The statistical distribution of nucleotide clusters for 11 chromosomes is characterized by the scaling behavior of P（S） ∝ e^-αs＇ where S represents nucleotide cluster size. The cluster-size distribution P（S1＋S2） with the total size of sequential C-G cluster and A-T cluster S1＋S2 were also studied. P（S1＋S2） follows exponential decay. There does not exist the case of large C-G cluster following large A-T cluster or large A-T cluster following large C-G cluster. We also discuss the relatively random walk length function L（n） and the local compositional complexity of nucleotide sequences based on a new model. These investigations may provide some insight into nucleotide cluster of DNA sequence.  相似文献   

7.
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   

8.
In the application of the Satorra–Bentler scaling correction, the choices of normal-theory weight matrices (i.e., the model-predicted vs. the sample covariance matrix) in the calculation of the correction remains unclear. Different software programs use different matrices by default. This simulation study investigates the discrepancies due to the weight matrices in the robust chi-square statistics, standard errors, and chi-square-based model fit indexes. This study varies the sample sizes at 100, 200, 500, and 1,000; kurtoses at 0, 7, and 21; and degrees of model misspecification, measured by the population root mean square error of approximation (RMSEA), at 0, .03, .05, .08, .10, and .15. The results favor the use of the model-predicted covariance matrix because it results in less false rejection rates under the correctly specified model, as well as more accurate standard errors across all conditions. For the sample-corrected robust RMSEA, comparative fit index (CFI) and Tucker–Lewis index (TLI), 2 matrices result in negligible differences.  相似文献   

9.
Measures of word recognition (REC) and two component skills, phonological coding (PHON) and orthographic coding (ORTH), were subjected to multivariate behavioral genetic analysis. Data were obtained from a sample of identical and fraternal twin pairs wherein at least one member of each pair was reading disabled (RD), and from a sample of twins wherein both members of each pair read in the normal range. Confirmatory factor analysis was used to fit the genetic, common environmental, and specific environmental covariance components for REC, PHON, and ORTH within the RD and normal simples. The resulting heritability estimates for REC, PHON, and ORTH were 0.59, 0.41, and 0.05 in the RD sample, and 0.35, 0.52, and 0.20 in the normal sample. After dropping the nonsignificant common environment parameters from the models, the genetic correlations between REC and PHON and between REC and ORTH were respectively 0.81 and 0.45 in the RD sample, and 0.68 and 0.45 in the normal sample. Differences between the genetic correlations were significant in the RD sample (p<0.005), marginally significant in the normal sample (p<0.10), and highly significant in the combined sample (p<0.001), indicating that genetic influences on individual differences in REC are more strongly related to genetic variance in PHON than in ORTH. These results are consistent with previous demonstrations of substantial genetic covariance between the disabled group's deficits in REC and PHON, but not between REC and ORTH (Olson et al., 1989; Olson and Rack, 1990).  相似文献   

10.
Orlando and Thissen's S‐X 2 item fit index has performed better than traditional item fit statistics such as Yen's Q1 and McKinley and Mill's G2 for dichotomous item response theory (IRT) models. This study extends the utility of S‐X 2 to polytomous IRT models, including the generalized partial credit model, partial credit model, and rating scale model. The performance of the generalized S‐X 2 in assessing item model fit was studied in terms of empirical Type I error rates and power and compared to G2. The results suggest that the generalized S‐X 2 is promising for polytomous items in educational and psychological testing programs.  相似文献   

11.
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   

12.
A 2-stage robust procedure as well as an R package, rsem, were recently developed for structural equation modeling with nonnormal missing data by Yuan and Zhang (2012). Several test statistics that have been used for complete data analysis are employed to evaluate model fit in the 2-stage robust method. However, properties of these statistics under robust procedures for incomplete nonnormal data analysis have never been studied. This study aims to systematically evaluate and compare 5 test statistics, including a test statistic derived from normal-distribution-based maximum likelihood, a rescaled chi-square statistic, an adjusted chi-square statistic, a corrected residual-based asymptotical distribution-free chi-square statistic, and a residual-based F statistic. These statistics are evaluated under a linear growth curve model by varying 8 factors: population distribution, missing data mechanism, missing data rate, sample size, number of measurement occasions, covariance between the latent intercept and slope, variance of measurement errors, and downweighting rate of the 2-stage robust method. The performance of the test statistics varies and the one derived from the 2-stage normal-distribution-based maximum likelihood performs much worse than the other four. Application of the 2-stage robust method and of the test statistics is illustrated through growth curve analysis of mathematical ability development, using data on the Peabody Individual Achievement Test mathematics assessment from the National Longitudinal Survey of Youth 1997 Cohort.  相似文献   

13.
This experimental study examined the efficacy of a multicomponent reading intervention compared to a control condition on the reading comprehension of adolescent students with low reading comprehension (more than 1½ standard deviations below normative sample). Ninth‐grade students were randomly assigned to treatment (n = 25) and comparison (n = 19). Reading teachers provided instruction for 90‐min, five times every two weeks for approximately 80 sessions. Treatment effects for each outcome measure were estimated using repeated measure of analysis of covariance for measures of reading comprehension and fluency. Results indicate no statistically significant differences between treatment and comparison conditions. Repeated‐measures analyses of variance between students with lower and higher decoding skills indicated a statistically significant interaction between treatment condition and decoding ability on the WJ‐III PC and Bridge‐IT, with large effect sizes (ηp2 .16 and .12, respectively), indicating that treatment was differentially beneficial for students with higher decoding skills.  相似文献   

14.
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   

15.
The Math Essential Skill Screener–Elementary Version (MESS-E) is a screener devised to identify primary grade students at risk for math difficulties. Item analysis, interitem consistency, test–retest reliability, decision efficiency, and construct validity of the MESS-E were studied using four independent samples of boys and girls grades 1–3 (aged 6–8). Item analysis revealed median item difficulty of .64 and median item discrimination of .75. Interitem consistency was .92 (n = 171) and .94 (n = 711), while 30-day test–retest reliability was .86 (n = 125). Exploratory factor analysis indicated a one-factor solution accounting for 37% of observed variance. LISREL 7 confirmatory factor analysis procedures determined that the one-factor model fit the standardization sample data poorly (goodness-of-fit index = .729, χ2 to df ratio = 9.91). The MESS-E yielded concurrent validity coefficients (n = 171) of .74 with the Woodcock–Johnson: Tests of Achievement–Revised (WJ-R) Math Cluster, .80 with the Wide-Range Achievement Test–Revised (WRAT-R) Arithmetic subtest and .73 with the KeyMath-R Operations Area standard scores. A diagnostic efficiency study yielded a total predictive value (TPV) of .93, sensitivity = .98, specificity = .88, positive predictive power (PPP) = .89, negative predictive power (NPP) = .98, and incremental validity = 39%. The MESS-E displayed a slight tendency to overidentify children potentially at risk for math difficulties. © 1998 John Wiley & Sons, Inc.  相似文献   

16.
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   

17.
This article considers the implications for other noncentrality parameter-based statistics from Steiger's (1998) multiple sample adjustment to the root mean square error of approximation (RMSEA) measure. When a structural equation model is fitted simultaneously in more than 1 sample, it is shown that the calculation of the noncentrality parameter used in tests of approximate fit and in point and interval estimators of other noncentral fit statistics (except the expected cross-validation index) also requires a likeminded adjustment. Furthermore, it is shown that an adjustment is needed in multiple sample models for correctly calculating MacCallum, Browne, and Sugawara's (1996) approach to power analysis. The accuracy of these proposals is investigated and demonstrated in a small Monte Carlo study in which particular attention is paid to using appropriately constructed covariance matrices that give specified nonzero population discrepancy values under maximum likelihood estimation.  相似文献   

18.
The purpose of the present study was to explore the contribution of extracurricular coaching on high school teachers’ job satisfaction. Specifically, the study looked at how perceptions of the coaching environment (athlete relationships, colleague relationships and opportunities through coaching) influenced teachers’ perceptions of stressors (athlete-related and workload-related) and coaching efficacy, and how this in-turn influenced teachers’ job satisfaction. The sample examined 2949 teachers from across Canada who volunteered as high school sport coaches, above and beyond their regular teaching load. The results supported that the data fit the model well (SBχ2(264) = 973.36, p < .001, SRMR = .08, CFI = .91, TLI = .90, RMSEA = .055 CI95 [.052, .059]) and that teachers who reported a positive coaching environment had increased coaching efficacy and decreased perceptions of athlete-related and workload-related stressors. Increased coaching efficacy predicted higher job satisfaction, while increased perceptions of stressors predicted lower job satisfaction.  相似文献   

19.
Up-conversion processes for the blue, green and red emissions were found two-photon phenomenon, known as the cooperative phenomenon. This phenomenon was assisted by Nd3+ → Yb3+ → Ho3+ energy transfer. The strong green emission due to the Ho3+ : (5F4, 5S2)→ 5I8 transitions was observed in Nd3+-Ho3+ co-doped ZrF4-based fluoride glasses under 800 nm excitation. As an attempt to enhance Ho3+ up-conversion luminescences in the Nd3+ – Ho3+ co-doped ZrF4-based glasses, Yb3+ ions were added to the glasses. As a result it was found that, in 800 nm excitation of 60 ZrF4. 30BaF2. (8-x)LaF3. lNdF3. xYbF3. 1HoF3 glasses (x=0 to 7), sensitized up-conversion luminescences are observed at around 490 nm (blue), 545 nm (green), and 650 nm (red), which correspond to the Ho3+ : 5F3 → 5I8, ( 5F4, 5S2)→5I8 and 5F5→ 5I8 transitions respectively. The intensities of the green and red emissions in a 3 mol % YbF3-containing glass were about 50 times stronger than those glasses without YbF3. This is based on sensitization due to Yb3+ ions. In particular, the green emission was extremely strong and the Nd3+-Yb3+-Ho3+ co-doped ZrF4-based glasses have a high possibility of realizing a green up-conversion laser glass. In this paper the up-conversion mechanism in the glasses is discussed in detail.  相似文献   

20.
In this study, liquid-phase aerobic oxidation of toluene catalyzed by Mn–Mo oxide was conducted in a 1.0 L batch reactor. The macroscopic kinetics of toluene consumption and benzaldehyde generation at 413–443 K were obtained from a combination of experimental observation and hypothetical models. The results clearly showed that both the oxidation rate of toluene and generation rate of the aromatic product were proportional to the concentration of the substrate, the partial pressure of oxygen and the surface area of the catalyst. The energy barrier of toluene oxidation to benzyl alcohol was the highest(≈ 81 kJ mol~(-1)), while that of benzyl alcohol oxidation to benzaldehyde was the lowest(≈ 57 kJ mol~(-1)). Moreover, the activation energy of further oxidation of benzaldehyde in an acetic acid solvent was only slightly lower(≈ 1.9 kJ mol~(-1)) than that of toluene oxidation. Significantly, the transformation of benzyl alcohol indeed contributed to the generation of benzaldehyde and this step conformed to a first-order parallel-consecutive model. Increased reaction temperature and residence time favored the transformation of benzyl alcohol to benzaldehyde. In addition, doping with molybdenum at Mn/Mo = 3/1 enhanced the catalytic performance of the heterogeneous catalyst and was attributed to the presence of a synergetic effect between different metal cations. Regarding the microscopic kinetics, the LH-OS-ND mechanism(Langmuir–Hinshelwood adsorption of reagents on the same type of active sites and non-dissociative adsorption of oxygen) was verified as responsible for the heterogeneous oxidation of toluene. Oxygen and benzaldehyde were weakly adsorbed(Δ H_(ads,Oxy) ≈~(-1)5 kJ mol~(-1), Δ H _(ads)0,Bald) ≈-30 kJ mol~(-1)), but showed strong mobility(Δ S_(ads,Oxy) ≈-22 J mol~(-1) K~(-1)), Δ S_(ads,Bald) ≈-39 J mol~(-1) K~(-1)). The fundamental intrinsic rates were deduced based on the LH-OS-ND mechanism and showed great consistency with the macroscopic results.  相似文献   

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