prior_check | R Documentation |
Perform prior predictive checks on a greta model object
prior_check(y, fun = "mean", probs = c(0.1, 0.9), nsim = 100)
y |
A greta array of the response variable |
fun |
A character, the name of the function to apply to the simulated response values, default is "mean". Custom functions can also be passed, see examples. |
probs |
A vector of two numeric, the lower and upper bound of the predictive interval |
nsim |
A numeric, the number of simulation draws, default is 100 |
Prior predictive checks allow a better tuning of the prior distribution of the model parameters by checking simulated new draws of the response. For instance, if we want to model the speed of migratory birds, we do not expect the maximum value of simulated draws from the priors to be beyond 100 of km/h.
A character string of the form: XX of the nsim simulated response from the prior distributions had a fun value between XX and XX.
## Not run: # a simple lm example intercept <- normal(0, 1) slope <- normal(0, 1) sd_resid <- cauchy(0, 1, truncation = c(0, 100)) x <- runif(100) y <- as_data(rnorm(100, 1 + 2 * x, 1)) linpred <- intercept + slope * x distribution(y) <- normal(linpred, sd_resid) prior_check(y) # can also use custom function, like counting number # of zero observations to check for zero-inflation count0 <- function(x){ sum(x==0) } # a poisson regression intercept <- normal(0, 1) slope <- normal(0, 1) x <- runif(100) y <- as_data(rpois(100, exp(0.001 + 1 * x, 1)) linpred <- intercept + slope * x distribution(y) <- poisson(linpred) prior_check(y, fun = "count0") ## End(Not run)
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