psych (version 1.0-77)

structure.graph: 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

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

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.

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)}