# ECV_SG: ECV_SG In BifactorIndicesCalculator: Bifactor Indices Calculator

## Description

Computes an ECV index for all factors which can be interpreted as the proportion of common variance of all items which is due to the specific factor; `ECV_SG` should be read 'ECV of a specific factor with respect to the general factor.' Here, ECV is computed with respect to the items of the general factor using the specific factor loadings in the numerator; Stucky and Edelen (2015, p. 199) refer to this index simply as 'specific-dimension ECV.' Note that `ECV_SG` of the general factor is simply the ECV. In the Excel version of the Bifactor Indices Calculator (Dueber, 2017), this form of ECV is referred to as 'ECV (S&E).' `ECV_SG` is called by `bifactorIndices` and the various convenience functions for exploratory models and/or Mplus output, which are the only functions in this package intended for casual users.

## Usage

 `1` ```ECV_SG(Lambda) ```

## Arguments

 `Lambda` is a matrix of factor loadings. Be sure that all factors have the same variance before calling this function.

## Value

A vector of ECVs for all factors

## References

Dueber, D. M. (2017). Bifactor Indices Calculator: A Microsoft Excel-based tool to calculate various indices relevant to bifactor CFA models. doi: 10.13023/edp.tool.01

Stucky, B. D., & Edelen, M. O. (2015). Using hierarchical IRT models to create unidimensional measures from multidimensional data. In S. P. Reise & D. A. Revicki (Eds.), Handbook of item response theory modeling: Applications to typical performance assessment (pp.183-206). New York: Routledge.

`ECV_SS`, `ECV_GS`, `bifactorIndices`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15``` ```Lambda <- matrix(c(.82, .10, 0, 0, .77, .35, 0, 0, .79, .32, 0, 0, .66, .39, 0, 0, .51, 0, .71, 0, .56, 0, .43, 0, .68, 0, .13, 0, .60, 0, .50, 0, .83, 0, 0, .47, .60, 0, 0, .27, .78, 0, 0, .28, .55, 0, 0, .75), ncol = 4, byrow = TRUE) colnames(Lambda) <- c("General", "SF1", "SF2", "SF3") ECV_GS(Lambda) ```