# ECV_GS: ECV_GS In BifactorIndicesCalculator: Bifactor Indices Calculator

## Description

Computes an ECV index for all factors which can be interpreted as the proportion of common variance of the items in each specific factor which is due to the general factor; `ECV_GS` should be read 'ECV of the general factor with respect to a specific factor.' Here, ECV is computed only with respect to the items of a specific factor using the general factor loadings in the numerator; Stucky and Edelen (2015, p. 201) refer to this index as the 'within-domain ECV' for the specific factor. In the Excel version of the bifactor indices calculator (Dueber, 2017), this index is not computed.

## Usage

 `1` ```ECV_GS(Lambda) ```

## Arguments

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

## Details

`ECV_GS` 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.

## 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_SG`, `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) ```