structure.graph {psych}R Documentation

Draw a structural equation model specified by two measurement models and a structural model

Description

Graphic presentations of structural equation models are a very useful way to conceptualize sem and confirmatory factor models. Given a measurement model on x (xmodel) and on y (ymodel) as well as a path model connecting x and y (phi), draw the graph. If ymodel is not specified, just draw the measurement model (xmodel + phi).

Perhaps even more usefully, the function returns a model appropriate for running directly in the sem package written by John Fox.

Input can be specified as matrices or the output from factanal, factor.pa, or a rotation package such as GPArotation.

For symbolic graphs, the input matrices can be character strings or mixtures of character strings and numeric vectors.

As an option, for those without Rgraphviz installed, structure.sem will just create the sem model and skip the graph.

Usage

structure.graph(fx,  Phi = NULL,fy = NULL, out.file = NULL, labels = NULL, cut = 0.3, errors=TRUE, simple=TRUE,regression=FALSE, size = c(8, 6), node.font = c("Helvetica", 14), edge.font = c("Helvetica", 10), rank.direction = c("RL", "TB", "LR", "BT"), digits = 1, title = "Structural model", ...)
structure.sem(fx,  Phi = NULL, fy = NULL,out.file = NULL, labels = NULL, cut = 0.3, errors=TRUE, simple=TRUE,regression=FALSE)

Arguments

fx a factor model on the x variables.
Phi A matrix of directed relationships. Lower diagonal values are drawn. If the upper diagonal values match the lower diagonal, two headed arrows are drawn. For a single, directed path, just the value may be specified.
fy a factor model on the y variables (can be empty)
out.file name a file to send dot language instructions.
labels variable labels if not specified as colnames for the matrices
cut Draw paths for values > cut
errors draw an error term for observerd variables
simple Just draw one path per x or y variable
regression Draw a regression diagram (observed variables cause Y)
size page size of graphic
node.font font type for graph
edge.font font type for graph
rank.direction Which direction should the graph be oriented
digits Number of digits to draw
title Title of graphic
... other options to pass to Rgraphviz

Details

Boths function return a matrix of commands suitable for using in the sem package.

The structure.graph output can be directed to an output file for post processing using the dot graphic language.

Value

sem a model matrix (partially) ready for input to John Fox's sem package. It is of class ``mod" for prettier output.
dotfile If out.file is specified, a dot language file suitable for using in a dot graphics program such as graphviz or Omnigraffle.


A graphic structural diagram in the graphics window

Author(s)

William Revelle

See Also

fa.graph, omega.graph, sim.structural

Examples

fx <- matrix(c(.9,.8,.6,rep(0,4),.6,.8,-.7),ncol=2)
fy <- matrix(c(.6,.5,.4),ncol=1)
Phi <- matrix(c(1,0,0,0,1,0,.7,.7,1),ncol=3,byrow=TRUE)
if(require(Rgraphviz)) { f1 <- structure.graph(fx,Phi,fy)  } else {f1 <- structure.sem(fx,Phi,fy)}

#symbolic input
X2 <- matrix(c("a",0,0,"b","e1",0,0,"e2"),ncol=4)
colnames(X2) <- c("X1","X2","E1","E2")
phi2 <- diag(1,4,4)
phi2[2,1] <- phi2[1,2] <- "r"
if(require(Rgraphviz)) { f2 <- structure.graph(X2,Phi=phi2,errors=FALSE)  } else {f2 <- structure.sem(X2,Phi=phi2,errors=FALSE) }

#symbolic input with error 
X2 <- matrix(c("a",0,0,"b"),ncol=2)
colnames(X2) <- c("X1","X2")
phi2 <- diag(1,2,2)
phi2[2,1] <- phi2[1,2] <- "r"
if(require(Rgraphviz)) { f3 <- structure.graph(X2,Phi=phi2)  } else {f3 <- structure.sem(X2,Phi=phi2)}

#and yet another one
X6 <- matrix(c("a","b","c",rep(0,6),"d","e","f"),nrow=6)
colnames(X6) <- c("L1","L2")
rownames(X6) <- c("x1","x2","x3","x4","x5","x6")
Y3 <- matrix(c("u","w","z"),ncol=1)
colnames(Y3) <- "Y"
rownames(Y3) <- c("y1","y2","y3")
phi21 <- matrix(c(1,0,"r1",0,1,"r2",0,0,1),ncol=3)
colnames(phi21) <- rownames(phi21) <-  c("L1","L2","Y")
if(require(Rgraphviz)) {f4 <- structure.graph(X6,phi21,Y3,title="Structural model")} else {f4 <- structure.sem(X6,phi21,Y3)}

# and finally, a regression model
X7 <- matrix(c("a","b","c","d","e","f"),nrow=6)
if(require(Rgraphviz)) {f5 <- structure.graph(X7,regression=TRUE)}

#and a really messy regession model
x8 <- c("b1","b2","b3")
r8 <- matrix(c(1,"r12","r13","r12",1,"r23","r13","r23",1),ncol=3)
if(require(Rgraphviz)) {f6<- structure.graph(x8,Phi=r8,regression=TRUE)}

[Package psych version 1.0-67 Index]