# vanishingTetrads: List Implied Vanishing Tetrads In dagitty: Graphical Analysis of Structural Causal Models

## Description

Interpret the given graph as a structural equation model and list all the vanishing tetrads that it implies.

## Usage

 `1` ```vanishingTetrads(x, type = NA) ```

## Arguments

 `x` the input graph, a DAG. `type` restrict output to one level of Kenny's tetrad typology. Possible values are "within" (homogeneity within constructs; all four variables have the same parents), "between" (homogeneity between constructs; two pairs of variables each sharing one parent) and "epistemic" (consistency of epistemic correlations; three variables have the same parent). By default, all tetrads are listed.

## Value

a data frame with four columns, where each row of the form i,j,k,l means that the tetrad Cov(i,j)Cov(k,l) - Cov(i,k)Cov(j,l) vanishes (is equal to 0) according to the model.

## References

Kenny, D. A. (1979), Correlation and Causality. Wiley, New York.

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10``` ```# Specify two-factor model with 4 indicators each g <- dagitty("dag{{x1 x2 x3 x4} <- x <-> y -> {y1 y2 y3 y4}}") latents(g) <- c("x","y") # Check how many tetrads are implied nrow(vanishingTetrads(g)) # Check how these distribute across the typology nrow(vanishingTetrads(g,"within")) nrow(vanishingTetrads(g,"between")) nrow(vanishingTetrads(g,"epistemic")) ```

dagitty documentation built on Jan. 21, 2021, 5:07 p.m.