Hello

I am trying to fit an ordinal model using brms with default priors. To my surprise I received messages that initial values have been rejected because the log probability evaluates to log(0). After many initialization attempts for each chain the sampling does eventually start. However, I am concerned about the rejections. Am I doing something wrong? This is my code:

T1$Rating <-factor(T1$Rating, ordered=TRUE)

family_1B ← brmsfamily(family = “cumulative”, link = “probit”)

formula_1B ← bf(Rating | thres(gr = SubjID) ~ 1 + TrialType + (1 | TrialType:StimType) + (0 + TrialType | SubjID))

fit1B ← brm(data = T1, family = family_1B, formula = formula_1B)

There are 24,192 observations in T1. Each row contains the following:

- Rating consists of numbers 1, 2, 3, and 4
- SubjID consists of string identifiers for each of the 14 subjects
- TrialType consists of string identifiers for each of the 3 different trial types
- StimType consists of string identifiers for each of the 3*18=54 different stimuli (18 per TrialType)

I added " | thres(gr = SubjID) " in an attempt to deal with subjects’ different response styles

Why are the initial values rejected? Is this normal? Should I be worried?

*brms version 2.19.0