MCMCregress  R Documentation 
This function generates a sample from the posterior distribution of a linear regression model with Gaussian errors using Gibbs sampling (with a multivariate Gaussian prior on the beta vector, and an inverse Gamma prior on the conditional error variance). The user supplies data and priors, and a sample from the posterior distribution is returned as an mcmc object, which can be subsequently analyzed with functions provided in the coda package.
MCMCregress( formula, data = NULL, burnin = 1000, mcmc = 10000, thin = 1, verbose = 0, seed = NA, beta.start = NA, b0 = 0, B0 = 0, c0 = 0.001, d0 = 0.001, sigma.mu = NA, sigma.var = NA, marginal.likelihood = c("none", "Laplace", "Chib95"), ... )
formula 
Model formula. 
data 
Data frame. 
burnin 
The number of burnin iterations for the sampler. 
mcmc 
The number of MCMC iterations after burnin. 
thin 
The thinning interval used in the simulation. The number of MCMC iterations must be divisible by this value. 
verbose 
A switch which determines whether or not the progress of the
sampler is printed to the screen. If 
seed 
The seed for the random number generator. If NA, the Mersenne
Twister generator is used with default seed 12345; if an integer is passed
it is used to seed the Mersenne twister. The user can also pass a list of
length two to use the L'Ecuyer random number generator, which is suitable
for parallel computation. The first element of the list is the L'Ecuyer
seed, which is a vector of length six or NA (if NA a default seed of

beta.start 
The starting values for the β vector. This can either be a scalar or a column vector with dimension equal to the number of betas. The default value of of NA will use the OLS estimate of β as the starting value. If this is a scalar, that value will serve as the starting value mean for all of the betas. 
b0 
The prior mean of β. This can either be a scalar or a column vector with dimension equal to the number of betas. If this takes a scalar value, then that value will serve as the prior mean for all of the betas. 
B0 
The prior precision of β. This can either be a scalar or a square matrix with dimensions equal to the number of betas. If this takes a scalar value, then that value times an identity matrix serves as the prior precision of beta. Default value of 0 is equivalent to an improper uniform prior for beta. 
c0 
c_0/2 is the shape parameter for the inverse Gamma prior on σ^2 (the variance of the disturbances). The amount of information in the inverse Gamma prior is something like that from c_0 pseudoobservations. 
d0 
d_0/2 is the scale parameter for the inverse Gamma prior on σ^2 (the variance of the disturbances). In constructing the inverse Gamma prior, d_0 acts like the sum of squared errors from the c_0 pseudoobservations. 
sigma.mu 
The mean of the inverse Gamma prior on σ^2. sigma.mu and sigma.var allow users to choose the inverse Gamma prior by choosing its mean and variance. 
sigma.var 
The variacne of the inverse Gamma prior on σ^2. sigma.mu and sigma.var allow users to choose the inverse Gamma prior by choosing its mean and variance. 
marginal.likelihood 
How should the marginal likelihood be calculated?
Options are: 
... 
further arguments to be passed. 
MCMCregress
simulates from the posterior distribution using standard
Gibbs sampling (a multivariate Normal draw for the betas, and an inverse
Gamma draw for the conditional error variance). The simulation proper is
done in compiled C++ code to maximize efficiency. Please consult the coda
documentation for a comprehensive list of functions that can be used to
analyze the posterior sample.
The model takes the following form:
y_i = x_i ' β + \varepsilon_{i}
Where the errors are assumed to be Gaussian:
\varepsilon_{i} \sim \mathcal{N}(0, σ^2)
We assume standard, semiconjugate priors:
β \sim \mathcal{N}(b_0,B_0^{1})
And:
σ^{2} \sim \mathcal{G}amma(c_0/2, d_0/2)
Where β and σ^{2} are assumed a priori independent. Note that only starting values for β are allowed because simulation is done using Gibbs sampling with the conditional error variance as the first block in the sampler.
An mcmc object that contains the posterior sample. This object can be summarized by functions provided by the coda package.
Andrew D. Martin, Kevin M. Quinn, and Jong Hee Park. 2011. “MCMCpack: Markov Chain Monte Carlo in R.”, Journal of Statistical Software. 42(9): 121. doi: 10.18637/jss.v042.i09.
Siddhartha Chib. 1995. “Marginal Likelihood from the Gibbs Output.” Journal of the American Statistical Association. 90: 13131321.
Robert E. Kass and Adrian E. Raftery. 1995. “Bayes Factors.” Journal of the American Statistical Association. 90: 773795.
Daniel Pemstein, Kevin M. Quinn, and Andrew D. Martin. 2007. Scythe Statistical Library 1.0. http://scythe.lsa.umich.edu.
Martyn Plummer, Nicky Best, Kate Cowles, and Karen Vines. 2006. “Output Analysis and Diagnostics for MCMC (CODA)”, R News. 6(1): 711. https://CRAN.Rproject.org/doc/Rnews/Rnews_20061.pdf.
plot.mcmc
, summary.mcmc
,
lm
## Not run: line < list(X = c(2,1,0,1,2), Y = c(1,3,3,3,5)) posterior < MCMCregress(Y~X, b0=0, B0 = 0.1, sigma.mu = 5, sigma.var = 25, data=line, verbose=1000) plot(posterior) raftery.diag(posterior) summary(posterior) ## End(Not run)
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