- Operating System: Mac OSX
- brms Version: 2.30

I’m attempting to do a multilevel mediation analysis. The dv is a likert scale response which I am modeling with a cumulative distribution (logit link). The mediator is categorical (Yes / No). When calculating the ab path, I am wondering if I can multiply the a and b coefficients directly (as below).

Knowledge_Judgment_mod <- bf(KnowledgeResponse ~ Condition + CounterfactualResponse + (1|Subject), family = “cumulative”)

Counterfactual_mod <- bf(CounterfactualResponse ~ Condition + (1|Subject), family = “bernoulli”)

model1 <- brm(Knowledge_Judgment_mod +

Counterfactual_mod,

set_rescor(FALSE),

data=data1,

iter=3000,

warmup=1500,

control = list(adapt_delta = .90),

prior = c(set_prior(“normal(0,1)”, class = “b”)))

a <- posterior_samples(model1, pars = “CounterfactualResponse_ConditionSpecific”)

b <- posterior_samples(model1, pars = “KnowledgeResponse_CounterfactualResponse”)

a_b <- a*b

summary(a_b)

CI_Model1_Mediation <- quantile(a_b$b_CounterfactualResponse_ConditionSpecific, probs = c(.025,.975))

CI_Model1_Mediation