Random effects: partial pooling

Specifies the random-effect structure of an mm or hm block, mirroring the left-hand side of an lme4/brms ( ... | group ) term. The grouping is implied by the block's id() and therefore not repeated.

RE = TRUE            # shorthand for re(1)
re(1)                # random intercept
re(1 + x)            # intercept + slope on x (INDEPENDENT, the default)
re(1 + x, cor = TRUE)# intercept + slope, correlated (lme4/brms `|`) - opt-in
re(0 + x)            # slope only (also re(x - 1))
re(1, ar = TRUE)     # random walk over participation order
re(1, ar = year)     # random walk over calendar time (gap-scaled variance)

The default cor = FALSE deliberately diverges from brms's correlated default: the correlated draw is a real JAGS cost, and in mm() blocks the member random effects are only read through the weighted aggregate sum_k w_k u_k, so the correlation is rarely of interest and often weakly identified. Opt in with cor = TRUE (supported for a single slope, i.e. the 2x2 case).

Usage

re(x = 1, cor = FALSE, ar = FALSE)

Arguments

x

The effects expression: 1, 1 + var, 0 + var, or var - 1. For mm() blocks, slope variables are member-level columns; for hm() blocks they are main-level columns varying within the nesting units.

cor

Logical; if TRUE, intercept and slope get a joint bivariate-normal prior (correlated). Default FALSE (independent).

ar

Autoregressive random walk for the intercept across a unit's repeated participations/observations. FALSE (default): independent effects. TRUE: random walk over participation order, \(u_t \sim N(u_{t-1}, \sigma^2)\). An unquoted column name (e.g. ar = year): random walk over that (numeric) time variable, with the step variance scaled by the normalized time gaps, \(u_t \sim N(u_{t-1}, \sigma^2 \, \Delta_t / \bar\Delta)\) — equal spacing reproduces the ar = TRUE model, and \(\sigma\) keeps its per-average-step interpretation. Requires an intercept-only re(1); time values must be unique within each unit.

Value

A bml_re object.

See also

fe, mm, hm