Hi Paul!

Yes, there are methods in SEM to examine longitudinal change, see examples in Geiser's book: Data Analysis with Mplus, chapter 4.

Best

John-Kåre

Yes, it is possible. But it is advisable and ideally that two or more indicators are needed for measurement. Sometimes two aren't enough either

Structural equation modeling is a multivariate statistical analysis technique that is used to analyze structural relationships.  This technique is the combination of factor analysis and multiple regression analysis, and it is used to analyze the structural relationship between measured variables and latent constructs.  This method is preferred by the researcher because it estimates the multiple and interrelated dependence in a single analysis.  In this analysis, two types of variables are used endogenous variables and exogenous variables.  Endogenous variables are equivalent to dependent variables and are equal to the independent variable

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Goodluck

You use the single-items measure you have to "fix" the "loading" and the "error" termin (for example to 1.0 and 0.0 - the case of a "perfect" reliable item). Without this constraints SEM models are not able to estimate this parameters because this part of the model is no identified.

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Goodluck