Clarification on Entering IIV for Population Simulation in mrgsolve

[SravaniLanke]

Hi,

I am setting up a population simulation using mrgsolve, and I have a question regarding how to handle inter-individual variability (IIV). Should I enter the IIV reported as CV% directly in the Omega section, or should I convert the CV% to variance (omega^2) before inputting it?

Thank you for your help!

[kylebaron]

Hi @SravaniLanke -

The OMEGA block takes variances for on-diagonal elements. So if you are entering this information yourself (e.g. pulling values from a publication), then convert %CV to variance before inputting. The off-diagonal elements take covariances or you can optionally enter those as correlations (see the @correlation block option)

library(mrgsolve)
#> 
#> Attaching package: 'mrgsolve'
#> The following object is masked from 'package:stats':
#> 
#>     filter
mod <- house()

library(mrgsolve)
mod <- '
$OMEGA @corr
1
0.5 2
'
mod <- mcode("corr", mod)
#> Building corr ...
#> done.
omat(mod)
#> $...
#>          [,1]      [,2]
#> 1:  1.0000000 0.7071068
#> 2:  0.7071068 2.0000000
cov2cor(as.matrix(omat(mod)))
#>      [,1] [,2]
#> [1,]  1.0  0.5
#> [2,]  0.5  1.0

^{Created on 2024-09-24 with reprex v2.1.1}

Kyle

[SravaniLanke]

Thank You Kyle.
I only have IIV for one parameter, So can I still use the CV% in the correlation matrix.

Thank you

[kylebaron]

If OMEGA is 1x1, then your only OMEGA element is on the diagonal and you'll have to enter that as a variance, converting from CV%.