apollo_deltaMethod {apollo}  R Documentation 
Delta method for Apollo models
Description
Applies the Delta method to calculate the standard errors of transformations of parameters.
Usage
apollo_deltaMethod(model, deltaMethod_settings)
Arguments
model 
Model object. Estimated model object as returned by function apollo_estimate. 
deltaMethod_settings 
List. Contains settings for this function. User input is required for all settings except those with a default or marked as optional.

Details
apollo_deltaMethod
can be used in two ways. The first and recommended way is to provide an
element called expression
inside its argument deltaMethod_settings
. expression
should contain the expression or expressions for which the standard error is/are to be calculated, as text. For
example, to calculate the ratio between parameters b1 and b2, expression=c(vtt="b1/b2")
should be used.
The second method is to provide the name of a specific operation inside deltaMethod_settings
.
The following five operations are supported.

sum
: Calculates the s.e. ofparName1
+parName2

diff
: Calculates the s.e. ofparName1
parName2
andparName2
parName1

prod
: Calculates the s.e. ofparName1
*parName2

ratio
: Calculates the s.e. ofparName1
/parName2
andparName2
/parName1

exp
: Calculates the s.e. ofexp(parName1)

logistic
: If onlyparName1
is provided, it calculates the s.e. ofexp(parName1)/(1+exp(parName1))
and1/(1+exp(parName1))
. IfparName1
andparName2
are provided, it calculatesexp(par_i)/(1+exp(parName1)+exp(parName2))
for i=1, 2, and 3 (par_3 = 1). 
lognormal
: Calculates the mean and s.d. of a lognormal distribution based on the mean (parName1
) and s.d. (parName2
) of the underlying normal.
By default, apollo_deltaMethod
uses the robust covariance matrix. However, the user can change this through the varcov
setting.
Value
Matrix containing value, s.e. and tratio resulting from the requested expression or operation. This is also printed to screen.