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Structured prior specifications

Source: R/priors.R
prior.Rd

Specify priors brms-style: a distribution call plus a parameter class, optionally narrowed to a single coefficient (coef) or block (group). Distributions are written on the natural (standard-deviation) scale and translated to JAGS's precision parameterization automatically.


prior(normal(0, 10),    class = "b")                      # all fixed coefficients
prior(normal(0, 1),     class = "b", coef = "education")  # one coefficient
prior(exponential(1),   class = "sd")                     # RE standard deviations
prior(lkj(2),           class = "cor")                    # RE correlation (re(cor=TRUE))
prior(student_t(3,0,5), class = "Intercept")
prior(normal(0, 1),     class = "w")                      # weight-model parameters
prior(uniform(0, 1),    class = "fn", coef = "c")         # fn shape parameters

Combine several with c() and pass as bml(..., prior = c(...)). Raw JAGS strings remain a power-user escape hatch: character elements such as "b.fn.1[1] ~ dnorm(0, 0.1)" are passed through untranslated.

Usage

prior(dist, class = "b", coef = "", group = "")

Arguments

dist

A distribution call. Supported: normal(mu, sigma), student_t(nu, mu, sigma), cauchy(mu, sigma), exponential(rate), gamma(shape, rate), uniform(lower, upper), lkj(eta) (class "cor" only). Scale parameters are standard deviations, not precisions.

class

Parameter class. One of:

  • "Intercept": the main intercept

  • "b": fixed coefficients (main-formula terms and block features); narrow with coef (term label, e.g. "education" or a feature name like "A_x")

  • "sd": random-effect standard deviations; narrow with group ("mm"/"hm" or a block id like "mm.1") and coef ("Intercept" or a slope variable)

  • "cor": the RE intercept-slope correlation (only exists when the user opts into re(..., cor = TRUE)) — use lkj(eta)

  • "sigma": the Gaussian residual SD

  • "shape": the Weibull shape parameter

  • "w": weight-model parameters (free symbols in w())

  • "fn": fn() shape parameters (c, kappa, p, DSL free symbols); narrow with coef

coef

Optional coefficient/parameter name to narrow the prior to.

group

Optional block identifier (e.g. "mm.1", "hm.2", or just "mm"/"hm").

Value

A bml_prior data frame (one row per prior); combine with c().

See also

get_prior, bml