I analyzed a data matrix using the Rasch model but I have the next problem: I need to inverse the sign of every estimated item difficulty to have a credible value. For example, if brm function return me a value of .9 for a specific item, I have to inverse the sign so the value of -.9 is the good one. Anybody knows how I can fix this with the next code?

Thanks!

formula15 <- bf(Xb15 ~ 1 + (1 | It15) + (1 | P15))

prior15 <- prior(“normal(0, 3)”, class = “sd”, group = “It15”) + prior(“normal(0, 3)”, class = “sd”, group = “P15”)

fit15 <- brm(formula = formula15,

data = X15,

family = brmsfamily(“bernoulli”,“logit”),

prior = prior15)