I am running a simple ACE model with covariates (e.g., sex, age). Now I am trying to impute missing covariate data using full information maximum likelihood (FILM) (as described here: https://openmx.ssri.psu.edu/docs/OpenMx/2.0.0-3838/FIML_RowFit.html).
To do this, I used an example script that was posted earlier by Mike Neale (https://openmx.ssri.psu.edu/sites/default/files/UnivariateTwinAnalysis_MatrixRaw-3.R) as a response to a post in this forum (https://openmx.ssri.psu.edu/thread/554). To get missing values, I added the following code to the script before I run the ACE including covariates model:
dzData[1:3,3] <- NA #delete 3 datapoints from age covariate (first twin)
However, I got the following error message:
Error in runHelper(model, frontendStart, intervals, silent, suppressWarnings, :
Error: NA value for a definition variable is Not Yet Implemented.
which, basically says that it is not possible to use FILM to impute missing data in covariates if I understand it correctly.
As I was told by a reviewer that it is possible to use FILM to impute missing covariate data, I however wanted to be sure that I run the analysis in the right way. Is there for example a command or option I didn't use, or am I using code that is too old? Or is FILM, indeed, only possible to use for the phenotypic (dependent) variables? And if so, are there any alternatives to listwise deletion?
I installed the latest version of OpenMx, using source('https://openmx.ssri.psu.edu/getOpenMx.R') and I am using R version 3.1.2.
Thank you so much for you time and effort.
Kind regards,
Inga Schwabe