Negative shrinkage?

Hello, I get a really weird negative eta shrinkage in my PopPK modeling exercise (FOCE-ELS engine). Is the shrinkage incorrectly estimated? Thanks, Dora

Dear Dora, Based on the standard formula that is used by pop pk modelers and our software (in the reference by Karlsson et al), it is possible to have a negative shrinkage value. A negative shrinkage is a very low shrinkage. Best regards, Emily