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Computational Issues Related To CFA



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Computational Issues Related To CFA Scale of observed variables important to keep them on a similar scale Convergence often related to starting values or the type of model being estimated Program stops because maximum number of iterations has been reached If no negative residual variances either increase the number of iterations or use the preliminary parameter estimates as starting values If there are large negative residual variances try better starting values Program stops before the maximum number of iterations has been reached Check if variables are on a similar scale Try new starting values Starting values the most important parameters to give starting values to are residual variances 129 Mplus MODEL Command For CFA MODEL command is used to describe the model to be estimated BY statement is used to define the latent variables or factors BY is short for measured by Example 1 standard parameterization MODEL f1 BY y1 y2 y3 f2 BY y4 y5 y6 Defaults Factor loading of first variable after BY is fixed to one Factor loadings of other variables are estimated Residual variances are estimated Residual covariances are fixed to zero Variances of factors are estimated Covariance between the exogenous factors is estimated 130 65 Mplus MODEL Command For CFA Continued Example 2 Alternative parameterization MODEL f1 BY y1 y2 y3 f2 BY y4 y5 y6 f1 1 f2 1 or f1 f2 1 131 EFA In A CFA Framework 132 66 EFA In A CFA Framework J reskog K G 1969 Purpose To obtain standard errors to determine if factor loadings are statistically significant To obtain modification indices to determine if residual covariances are needed to represent minor factors Use the same number of restrictions as an exploratory factor analysis model m2 Fix factor variances to one for m restrictions Fix factor loadings to zero for the remaining restrictions Find an anchor item for each factor select an item that has a large loading for the factor and small loadings for other factors Fix the loading of the anchor item to



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