spMisalignLM {spBayes}

Function for fitting multivariate Bayesian spatial regression models to misaligned data

Description

The function spMisalignLM fits Gaussian multivariate Bayesian spatial regression models to misaligned data.

Usage

spMisalignLM(formula, data = parent.frame(), coords, 
      starting, tuning, priors, cov.model,
      amcmc, n.samples, verbose=TRUE, n.report=100, ...)

Arguments

formula

a list of q symbolic regression models to be fit. See example below.

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 spMisalignLM is called.

coords

a list of q n_i \times 2 matrices of the observation coordinates in R^2 (e.g., easting and northing) where i=(1,2,\ldots,q). .

starting

a list with tags corresponding to A, phi, nu, and Psi. The value portion of each tag is a vector that holds the parameter's starting values.

A is of length \frac{q(q+1)}{2} and holds the lower-triangle elements in column major ordering of the Cholesky square root of the spatial cross-covariance matrix.

phi and nu are of length q. The vector of residual variances Psi is also of length q.

tuning

a list with tags A, phi, nu, and Psi. The value portion of each tag defines the variance of the Metropolis sampler Normal proposal distribution. A is of length \frac{q(q+1)}{2} and Psi, phi, and nu are of length q.

priors

a list with tags beta.flat, K.iw, Psi.ig, phi.unif and nu.unif. The hyperparameters of the inverse-Wishart for the cross-covariance matrix K=AA' are passed as a list of length two, with the first and second elements corresponding to the df and q\times q scale matrix, respectively. The inverse-Gamma hyperparameters for the non-spatial residual variances are specified as a list Psi.ig of length two with the first and second list elements consisting of vectors of the q shape and scale hyperparameters, respectively. The hyperparameters of the Uniform phi.unif, and nu.unif are also passed as a list of vectors with the first and second list elements corresponding to the lower and upper support, respectively.

cov.model

a quoted keyword 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.

amcmc

a list with tags n.batch, batch.length, and accept.rate. Specifying this argument invokes an adaptive MCMC sampler see Roberts and Rosenthal (2007) for an explanation.

n.samples

the number of MCMC iterations. This argument is ignored if amcmc is specified.

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.

Details

Model parameters can be fixed at their starting values by setting their tuning values to zero.

Value

An object of class spMisalignLM, which is a list with the following tags:

p.theta.samples

a coda object of posterior samples for the defined parameters.

acceptance

the Metropolis sampling acceptance percent. Reported at batch.length or n.report intervals for amcmc specified and non-specified, respectively

The return object might include additional data used for subsequent prediction and/or model fit evaluation.

Author(s)

Andrew O. Finley [e-mail],
Sudipto Banerjee [e-mail]

References

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.

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.

Finley, A.O., S. Banerjee, and B.D. Cook. (2014) Bayesian hierarchical models for spatially misaligned data. Methods in Ecology and Evolution, 5:514–523.

Finley, A.O., H. Sang, S. Banerjee, and A.E. Gelfand. (2009) Improving the performance of predictive process modeling for large datasets. Computational Statistics and Data Analysis, 53:2873–2884.

Finley, A.O., S. Banerjee, A.R. Ek, and R.E. McRoberts. (2008) Bayesian multivariate process modeling for prediction of forest attributes. Journal of Agricultural, Biological, and Environmental Statistics, 13:60–83.

See Also

spMvLMspMisalignGLM

Examples

## Not run: 
rmvn <- function(n, mu=0, V = matrix(1)){
  p <- length(mu)
  if(any(is.na(match(dim(V),p)))){stop("Dimension problem!")}
  D <- chol(V)
  t(matrix(rnorm(n*p), ncol=p)%*%D + rep(mu,rep(n,p)))
}

set.seed(1)

##generate some data
n <- 100 ##number of locations
q <- 3 ##number of outcomes at each location
nltr <- q*(q+1)/2 ##number of triangular elements in the cross-covariance matrix

coords <- cbind(runif(n,0,1), runif(n,0,1))

##parameters for generating a multivariate spatial GP covariance matrix
theta <- rep(3/0.5,q) ##spatial decay

A <- matrix(0,q,q)
A[lower.tri(A,TRUE)] <- c(1,1,-1,1,0.5,0.25)
K <- A%*%t(A)
K ##spatial cross-covariance
cov2cor(K) ##spatial cross-correlation

C <- mkSpCov(coords, K, diag(0,q), theta, cov.model="exponential")

w <- rmvn(1, rep(0,nrow(C)), C) ##spatial random effects

w.a <- w[seq(1,length(w),q)]
w.b <- w[seq(2,length(w),q)]
w.c <- w[seq(3,length(w),q)]

##covariate portion of the mean
x.a <- cbind(1, rnorm(n))
x.b <- cbind(1, rnorm(n))
x.c <- cbind(1, rnorm(n))
x <- mkMvX(list(x.a, x.b, x.c))

B.1 <- c(1,-1)
B.2 <- c(-1,1)
B.3 <- c(-1,-1)
B <- c(B.1, B.2, B.3)

Psi <- c(0.1, 0.1, 0.1) ##non-spatial residual variance, i.e., nugget

y <- rnorm(n*q, x%*%B+w, rep(sqrt(Psi),n))

y.a <- y[seq(1,length(y),q)]
y.b <- y[seq(2,length(y),q)]
y.c <- y[seq(3,length(y),q)]

##subsample to make spatially misaligned data
sub.1 <- 1:50
y.1 <- y.a[sub.1]
w.1 <- w.a[sub.1]
coords.1 <- coords[sub.1,]
x.1 <- x.a[sub.1,]

sub.2 <- 25:75
y.2 <- y.b[sub.2]
w.2 <- w.b[sub.2]
coords.2 <- coords[sub.2,]
x.2 <- x.b[sub.2,]

sub.3 <- 50:100
y.3 <- y.c[sub.3]
w.3 <- w.c[sub.3]
coords.3 <- coords[sub.3,]
x.3 <- x.c[sub.3,]

##call spMisalignLM
q <- 3
A.starting <- diag(1,q)[lower.tri(diag(1,q), TRUE)]
n.samples <- 5000

starting <- list("phi"=rep(3/0.5,q), "A"=A.starting, "Psi"=rep(1,q))
tuning <- list("phi"=rep(0.5,q), "A"=rep(0.01,length(A.starting)), "Psi"=rep(0.1,q))
priors <- list("phi.Unif"=list(rep(3/0.75,q), rep(3/0.25,q)),
               "K.IW"=list(q+1, diag(0.1,q)), "Psi.ig"=list(rep(2,q), rep(0.1,q)))

m.1 <- spMisalignLM(list(y.1~x.1-1, y.2~x.2-1, y.3~x.3-1), 
                    coords=list(coords.1, coords.2, coords.3),
                    starting=starting, tuning=tuning, priors=priors, 
                    n.samples=n.samples, cov.model="exponential", n.report=100)

burn.in <- floor(0.75*n.samples)

plot(m.1$p.theta.samples, density=FALSE)

##recover regression coefficients and random effects
m.1 <- spRecover(m.1, start=burn.in)

round(summary(m.1$p.theta.recover.samples)$quantiles[,c(3,1,5)],2)
round(summary(m.1$p.beta.recover.samples)$quantiles[,c(3,1,5)],2)

##predict for all locations, i.e., observed and not observed
out <- spPredict(m.1, start=burn.in, thin=10, pred.covars=list(x.a, x.b,
x.c), 
                 pred.coords=list(coords, coords, coords))

##summary and check
quants <- function(x){quantile(x, prob=c(0.5,0.025,0.975))}

y.hat <- apply(out$p.y.predictive.samples, 1, quants)

##unstack and plot
y.a.hat <- y.hat[,1:n]
y.b.hat <- y.hat[,(n+1):(2*n)]
y.c.hat <- y.hat[,(2*n+1):(3*n)]

par(mfrow=c(1,3))
plot(y.a, y.a.hat[1,], xlab="Observed y.a", ylab="Fitted & predicted y.a",
     xlim=range(y), ylim=range(y.hat), main="")
arrows(y.a[-sub.1], y.a.hat[1,-sub.1], y.a[-sub.1], y.a.hat[2,-sub.1], length=0.02, angle=90)
arrows(y.a[-sub.1], y.a.hat[1,-sub.1], y.a[-sub.1], y.a.hat[3,-sub.1], length=0.02, angle=90)
lines(range(y.a), range(y.a))

plot(y.b, y.b.hat[1,], xlab="Observed y.b", ylab="Fitted & predicted y.b",
     xlim=range(y), ylim=range(y.hat), main="")
arrows(y.b[-sub.2], y.b.hat[1,-sub.2], y.b[-sub.2], y.b.hat[2,-sub.2], length=0.02, angle=90)
arrows(y.b[-sub.2], y.b.hat[1,-sub.2], y.b[-sub.2], y.b.hat[3,-sub.2], length=0.02, angle=90)
lines(range(y.b), range(y.b))

plot(y.c, y.c.hat[1,], xlab="Observed y.c", ylab="Fitted & predicted y.c",
     xlim=range(y), ylim=range(y.hat), main="")
arrows(y.c[-sub.3], y.c.hat[1,-sub.3], y.c[-sub.3], y.c.hat[2,-sub.3], length=0.02, angle=90)
arrows(y.c[-sub.3], y.c.hat[1,-sub.3], y.c[-sub.3], y.c.hat[3,-sub.3], length=0.02, angle=90)
lines(range(y.c), range(y.c))

## End(Not run)