Specify a Structural Equation Model
Description
Create the RAM specification of a structural equation model.
Usage
1 2 3 4  specify.model(file = "")
## S3 method for class 'mod'
print(x, ...)

Arguments
file 
The (quoted) file from which to read the model specification,
including the path to the file if it is not in the current directory. If

x 
An object of class 
... 
Ignored. 
Details
Each line of the RAM specification consists of three (unquoted) entries, separated by commas:
 1. Arrow specification:
This is a simple formula, of the form
A > B
or, equivalently,B < A
for a regression coefficient (i.e., a singleheaded or directional arrow);A <> A
for a variance orA <> B
for a covariance (i.e., a doubleheaded or bidirectional arrow). Here,A
andB
are variable names in the model. If a name does not correspond to an observed variable, then it is assumed to be a latent variable. Spaces can appear freely in an arrow specification, and there can be any number of hyphens in the arrows, including zero: Thus, e.g.,A>B
,A > B
, andA>B
are all legitimate and equivalent. 2. Parameter name:
The name of the regression coefficient, variance, or covariance specified by the arrow. Assigning the same name to two or more arrows results in an equality constraint. Specifying the parameter name as
NA
produces a fixed parameter. 3. Value:
start value for a free parameter or value of a fixed parameter. If given as
NA
,sem
will compute the start value.
Lines may end in a comment following \#
.
See sem
for further details on model specification.
Value
An object of class mod
, suitable as input for sem
.
Author(s)
John Fox jfox@mcmaster.ca
See Also
sem
Examples
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27  ## Not run:
model.dhp < specify.model()
RParAsp > RGenAsp, gam11, NA
RIQ > RGenAsp, gam12, NA
RSES > RGenAsp, gam13, NA
FSES > RGenAsp, gam14, NA
RSES > FGenAsp, gam23, NA
FSES > FGenAsp, gam24, NA
FIQ > FGenAsp, gam25, NA
FParAsp > FGenAsp, gam26, NA
FGenAsp > RGenAsp, beta12, NA
RGenAsp > FGenAsp, beta21, NA
RGenAsp > ROccAsp, NA, 1
RGenAsp > REdAsp, lam21, NA
FGenAsp > FOccAsp, NA, 1
FGenAsp > FEdAsp, lam42, NA
RGenAsp <> RGenAsp, ps11, NA
FGenAsp <> FGenAsp, ps22, NA
RGenAsp <> FGenAsp, ps12, NA
ROccAsp <> ROccAsp, theta1, NA
REdAsp <> REdAsp, theta2, NA
FOccAsp <> FOccAsp, theta3, NA
FEdAsp <> FEdAsp, theta4, NA
model.dhp
## End(Not run)
