spGLM {spBayes} | R Documentation |
The function spGLM
fits univariate stationary Bayesian
generalized linear spatial regression models. Given a set of knots, spGLM
fits a
predictive process model (see references below).
spGLM(formula, family="binomial", data = parent.frame(), coords, knots, starting, tuning, priors, cov.model, n.samples, verbose=TRUE, n.report=100, ...)
formula |
a symbolic description of the regression model to be fit. See example below. |
family |
currently only supports binomial and
poisson data using the logit and log link functions, respectively. |
data |
an optional data frame containing the variables in the
model. If not found in data, the variables are taken from
environment(formula) , typically the environment from which spGLM is called. |
coords |
an n x 2 matrix of the observation coordinates in R^2 (e.g., easting and northing). |
knots |
either a m x 2 matrix of the
predictive process knot coordinates in R^2 (e.g., easting and northing)
or a vector of length two or three with the first and second elements recording the
number of columns and rows in the desired knot grid. The third,
optional, element sets the offset of the outermost knots from the
extent of the coords extent. |
starting |
a list with each tag corresponding to a
parameter name. Valid list tags are beta , sigma.sq ,
phi , nu , and w . The value portion of each tag is the parameter's starting value. If the predictive
process is used then w must be of length m; otherwise,
it must be of length n. Alternatively, w can be set
as a scalar, in which case the value is repeated. |
tuning |
a list with each tag corresponding to a
parameter name. Valid list tags are beta , sigma.sq ,
phi , nu , and w . The value portion of each tag defines the variance of the Metropolis normal proposal distribution. The tuning value for beta can be a
vector of length p or the lower-triangle of the
pxp Cholesky square-root of the desired proposal variance matrix.
If the predictive process is used then w must be of length m; otherwise,
it must be of length n. Alternatively, w can be set
as a scalar, in which the value is repeated. |
priors |
a list with each tag corresponding to a
parameter name. Valid list tags are beta.flat , beta.normal , sigma.sq.ig ,
phi.unif , and nu.unif . simga.sq is assumed to follow an
inverse-Gamma distribution, whereas the spatial range phi
and smoothness nu parameters are assumed to follow Uniform
distributions. If beta.normal then covariate specific mean and variance hyperparameters are
passed as the first and second list elements, respectively. The
hyperparameters of the inverse-Gamma are
passed as a vector of length two, with the first and second elements corresponding
to the shape and scale, respectively. The hyperparameters
of the Uniform are also passed as a vector of length two with the first
and second elements corresponding to the lower and upper support,
respectively. |
cov.model |
a quoted key word that specifies the covariance
function used to model the spatial dependence structure among the
observations. Supported covariance model key words are:
"exponential" , "matern" , "spherical" , and
"gaussian" . See below for details. |
n.samples |
the number of MCMC iterations. |
verbose |
if TRUE , model specification and progress of the
sampler is printed to the screen. Otherwise, nothing is printed to
the screen. |
n.report |
the interval to report Metropolis acceptance and MCMC progress. |
... |
currently no additional arguments. |
An object of class spGLM
, which is a list with the following
tags:
coords |
the n x 2 matrix specified by
coords . |
knot.coords |
the m x 2 matrix as specified by knots . |
p.samples |
a coda object of posterior samples for the defined
parameters. |
acceptance |
the Metropolis sampling acceptance rate. |
sp.effects |
a matrix that holds samples from the posterior distribution of the spatial random effects. The rows of this matrix correspond to the n point observations and the columns are the posterior samples. |
The return object might include additional data used for subsequent prediction and/or model fit evaluation.
Andrew O. Finley finleya@msu.edu,
Sudipto Banerjee baner009@umn.edu
Finley, A.O., S. Banerjee, and R.E. McRoberts. (2008) A Bayesian approach to quantifying uncertainty in multi-source forest area estimates. Environmental and Ecological Statistics, 15:241–258.
Banerjee, S., A.E. Gelfand, A.O. Finley, and H. Sang. (2008) Gaussian Predictive Process Models for Large Spatial Datasets. Journal of the Royal Statistical Society Series B, 70:825–848.
Finley, A.O,. H. Sang, S. Banerjee, and A.E. Gelfand. (2008). Improving the performance of predictive process modeling for large datasets. Computational Statistics and Data Analysis, DOI: 10.1016/j.csda.2008.09.008
Banerjee, S., Carlin, B.P., and Gelfand, A.E. (2004). Hierarchical modeling and analysis for spatial data. Chapman and Hall/CRC Press, Boca Raton, Fla.
## Not run: ########################### ##Spatial poisson ########################### ##Generate count data n <- 100 coords <- cbind(runif(n,1,100),runif(n,1,100)) phi <- 3/75 sigma.sq <- 2 R <- sigma.sq*exp(-phi*as.matrix(dist(coords))) w <- mvrnorm(1, rep(0,n), R) x <- as.matrix(rep(1,n)) beta <- 0.1 y <- rpois(n, exp(x%*%beta+w)) ##Collect samples beta.starting <- coefficients(glm(y~x-1, family="poisson")) beta.tuning <- t(chol(vcov(glm(y~x-1, family="poisson")))) n.samples <- 25000 m.1 <- spGLM(y~1, family="poisson", coords=coords, starting= list("beta"=beta.starting, "phi"=0.06,"sigma.sq"=1, "w"=0), tuning= list("beta"=0.1, "phi"=0.01, "sigma.sq"=0.01, "w"=0.005), priors= list("beta.Flat", "phi.Unif"=c(0.03, 0.3), "sigma.sq.IG"=c(2, 1)), cov.model="exponential", n.samples=n.samples, verbose=TRUE, n.report=500) m.1$p.samples[,"phi"] <- 3/m.1$p.samples[,"phi"] burn.in <- 0.75*n.samples print(summary(mcmc(m.1$p.samples[burn.in:n.samples,]))) beta.hat <- mean(m.1$p.samples[burn.in:n.samples,1]) w.hat <- rowMeans(m.1$sp.effects[,burn.in:n.samples]) y.hat <-exp(x%*%beta.hat+w.hat) ##Take a look par(mfrow=c(1,2)) surf <- mba.surf(cbind(coords,y),no.X=100, no.Y=100, extend=TRUE)$xyz.est image(surf, main="obs") contour(surf, drawlabels=FALSE, add=TRUE) text(coords, labels=y, cex=1, col="blue") surf <- mba.surf(cbind(coords,y.hat),no.X=100, no.Y=100, extend=TRUE)$xyz.est image(surf, main="Fitted counts") contour(surf, drawlabels=FALSE, add=TRUE) text(coords, labels=round(y.hat,0), cex=1, col="blue") ########################### ##Spatial logistic ########################### ##Generate binary data n <- 50 coords <- cbind(runif(n,1,100),runif(n,1,100)) phi <- 3/50 sigma.sq <- 1 R <- sigma.sq*exp(-phi*as.matrix(dist(coords))) w <- mvrnorm(1, rep(0,n), R) x <- as.matrix(rep(1,n)) beta <- 0.1 p <- 1/(1+exp(-(x%*%beta+w))) y <- rbinom(n, 1, prob=p) ##Collect samples beta.starting <- coefficients(glm(y~x-1, family="binomial")) beta.tuning <- t(chol(vcov(glm(y~x-1, family="binomial")))) n.samples <- 50000 m.1 <- spGLM(y~1, family="binomial", coords=coords, starting= list("beta"=beta.starting, "phi"=0.06,"sigma.sq"=1, "w"=0), tuning= list("beta"=beta.tuning, "phi"=0.1, "sigma.sq"=0.1, "w"=0.01), priors= list("beta.Normal"=list(0,10), "phi.Unif"=c(0.03, 0.3), "sigma.sq.IG"=c(2, 1)), cov.model="exponential", n.samples=n.samples, verbose=TRUE, n.report=500) m.1$p.samples[,"phi"] <- 3/m.1$p.samples[,"phi"] burn.in <- 0.75*n.samples print(summary(mcmc(m.1$p.samples[burn.in:n.samples,]))) beta.hat <- mean(m.1$p.samples[burn.in:n.samples,1]) w.hat <- rowMeans(m.1$sp.effects[,burn.in:n.samples]) y.hat <- 1/(1+exp(-(x%*%beta.hat+w.hat))) ##Take a look par(mfrow=c(1,2)) surf <- mba.surf(cbind(coords,y),no.X=100, no.Y=100, extend=TRUE)$xyz.est image(surf, main="Observed") contour(surf, add=TRUE) points(coords[y==1,], pch=19, cex=1) points(coords[y==0,], cex=1) surf <- mba.surf(cbind(coords,y.hat),no.X=100, no.Y=100, extend=TRUE)$xyz.est image(surf, main="Fitted probabilities") contour(surf, add=TRUE) points(coords[y==1,], pch=19, cex=1) points(coords[y==0,], cex=1) ## End(Not run)