mcsamp: Generic Function to Run 'mcmcsamp()' in lme4

In arm: Data Analysis Using Regression and Multilevel/Hierarchical Models

Generic Function to Run ‘mcmcsamp()’ in lme4

Description

The quick function for MCMC sampling for lmer and glmer objects and convert to Bugs objects for easy display.

Usage

## Default S3 method:
mcsamp(object, n.chains=3, n.iter=1000, n.burnin=floor(n.iter/2), 
    n.thin=max(1, floor(n.chains * (n.iter - n.burnin)/1000)), 
    saveb=TRUE, deviance=TRUE, make.bugs.object=TRUE)
## S4 method for signature 'merMod'
 mcsamp(object, ...)

Arguments

object	mer objects from lme4
n.chains	number of MCMC chains
n.iter	number of iteration for each MCMC chain
n.burnin	number of burnin for each MCMC chain, Default is n.iter/2, that is, discarding the first half of the simulations.
n.thin	keep every kth draw from each MCMC chain. Must be a positive integer. Default is max(1, floor(n.chains * (n.iter-n.burnin) / 1000)) which will only thin if there are at least 2000 simulations.
saveb	if 'TRUE', causes the values of the random effects in each sample to be saved.
deviance	compute deviance for mer objects. Only works for lmer object
make.bugs.object	tranform the output into bugs object, default is TRUE
...	further arguments passed to or from other methods.

Details

This function generates a sample from the posterior distribution of the parameters of a fitted model using Markov Chain Monte Carlo methods. It automatically simulates multiple sequences and allows convergence to be monitored. The function relies on mcmcsamp in lme4.

Value

An object of (S3) class '"bugs"' suitable for use with the functions in the "R2WinBUGS" package.

Author(s)

Andrew Gelman [e-mail]; Yu-Sung Su [e-mail]

References

Andrew Gelman and Jennifer Hill, Data Analysis Using Regression and Multilevel/Hierarchical Models, Cambridge University Press, 2006.

Douglas Bates and Deepayan Sarkar, lme4: Linear mixed-effects models using S4 classes.

See Also

display, lmer, sim

Examples

## Here's a simple example of a model of the form, y = a + bx + error, 
## with 10 observations in each of 10 groups, and with both the intercept 
## and the slope varying by group.  First we set up the model and data.
##   
#   group <- rep(1:10, rep(10,10))
#   group2 <- rep(1:10, 10)
#   mu.a <- 0
#   sigma.a <- 2
#   mu.b <- 3
#   sigma.b <- 4
#   rho <- 0.56
#   Sigma.ab <- array (c(sigma.a^2, rho*sigma.a*sigma.b, 
#                    rho*sigma.a*sigma.b, sigma.b^2), c(2,2))
#   sigma.y <- 1
#   ab <- mvrnorm (10, c(mu.a,mu.b), Sigma.ab)
#   a <- ab[,1]
#   b <- ab[,2]
#   d <- rnorm(10)
#
#   x <- rnorm (100)
#   y1 <- rnorm (100, a[group] + b*x, sigma.y)
#   y2 <- rbinom(100, 1, prob=invlogit(a[group] + b*x))
#   y3 <- rnorm (100, a[group] + b[group]*x + d[group2], sigma.y)
#   y4 <- rbinom(100, 1, prob=invlogit(a[group] + b*x + d[group2]))
#
## 
## Then fit and display a simple varying-intercept model:
# 
#   M1 <- lmer (y1 ~ x + (1|group))
#   display (M1)
#   M1.sim <- mcsamp (M1)
#   print (M1.sim)
#   plot (M1.sim)
## 
## Then the full varying-intercept, varying-slope model:
## 
#   M2 <- lmer (y1 ~ x + (1 + x |group))
#   display (M2)
#   M2.sim <- mcsamp (M2)
#   print (M2.sim)
#   plot (M2.sim)
## 
## Then the full varying-intercept, logit model:
## 
#   M3 <- lmer (y2 ~ x + (1|group), family=binomial(link="logit"))
#   display (M3)
#   M3.sim <- mcsamp (M3)
#   print (M3.sim)
#   plot (M3.sim)
## 
## Then the full varying-intercept, varying-slope logit model:
## 
#   M4 <- lmer (y2 ~ x + (1|group) + (0+x |group), 
#        family=binomial(link="logit"))
#   display (M4)
#   M4.sim <- mcsamp (M4)
#   print (M4.sim)
#   plot (M4.sim)
#   
##
## Then non-nested varying-intercept, varying-slop model:
##
#   M5 <- lmer (y3 ~ x + (1 + x |group) + (1|group2))
#   display(M5)
#   M5.sim <- mcsamp (M5)
#   print (M5.sim)
#   plot (M5.sim)
      
 

arm documentation built on June 25, 2024, 1:14 a.m.