Hello everyone,
I am facing a bootstrap issue in Phoenix NLME after upgrading from version 8.5 to 8.8 and would appreciate insights from others who may have encountered similar behavior.
Background
I am working on a 2-sequence, 2-period crossover BE study with the following structure:
Each subject receives both Test and Reference
Period 1 → 50% subj first, 50% second formulation
Period 2 → 50% subj second, 50% first formulation after washout
Dataset includes all major columns:
USUBJIDN, TREATN, SequenceN, Period, TAD, AFRLT, Cobs, AMT, EVID, MDV
Data is sorted by USUBJIDN
Model initially used AFRLT (time after first dose):
Period 1: 0–24 h
Period 2: after washout (~168 h onward)
Model behavior
The base model fits without any issue, visual predictive check by TAD or AFRLT all ok. Convergence achieved for all model parameters.
In Phoenix 8.5, bootstrap ran successfully (tested with ~50 replicates)
After upgrading to Phoenix 8.8, running the same dataset , same model file (just simple re-run)and same parameters without any change also results in bootstrap failure.
Here is earlier output smapshot
Now Bootstrap error, without any Stratification, just replicate
It results below error without a single run
Now Bootstrap error, with Stratification as SequenceN
model runs up to 4 replication then
I would appreciate your input.
Thank you .