Simulate Single-Species Detection-Nondetection Data

The function simOcc simulates single-species occurrence data for simulation studies, power assessments, or function testing. Data can be optionally simulated with a spatial Gaussian Process in the occurrence portion of the model. Non-spatial random intercepts can also be included in the detection or occurrence portions of the occupancy model.

Usage

simOcc(J.x, J.y, n.rep, n.rep.max, beta, alpha, psi.RE = list(), 
       p.RE = list(), sp = FALSE, svc.cols = 1, cov.model, 
       sigma.sq, phi, nu, x.positive = FALSE, grid, ...)

Arguments

J.x: a single numeric value indicating the number of sites to simulate detection-nondetection data along the horizontal axis. Total number of sites with simulated data is \(J.x \times J.y\).
J.y: a single numeric value indicating the number of sites to simulate detection-nondetection data along the vertical axis. Total number of sites with simulated data is \(J.x \times J.y\).
n.rep: a numeric vector of length \(J = J.x \times J.y\) indicating the number of repeat visits at each of the \(J\) sites.
n.rep.max: a single numeric value indicating the maximum number of replicate surveys. This is an optional argument, with its default value set to max(n.rep). This can be used to generate data sets with different types of missingness (e.g., simulate data across 20 days (replicate surveys) but sites are only sampled a maximum of ten times each).
beta: a numeric vector containing the intercept and regression coefficient parameters for the occupancy portion of the single-species occupancy model.
alpha: a numeric vector containing the intercept and regression coefficient parameters for the detection portion of the single-species occupancy model.
psi.RE: a list used to specify the non-spatial random intercepts included in the occupancy portion of the model. The list must have two tags: levels and sigma.sq.psi. levels is a vector of length equal to the number of distinct random intercepts to include in the model and contains the number of levels there are in each intercept. sigma.sq.psi is a vector of length equal to the number of distinct random intercepts to include in the model and contains the variances for each random effect. If not specified, no random effects are included in the occupancy portion of the model.
p.RE: a list used to specify the non-spatial random intercepts included in the detection portion of the model. The list must have two tags: levels and sigma.sq.p. levels is a vector of length equal to the number of distinct random intercepts to include in the model and contains the number of levels there are in each intercept. sigma.sq.p is a vector of length equal to the number of distinct random intercepts to include in the model and contains the variances for each random effect. If not specified, no random effects are included in the detection portion of the model.
sp: a logical value indicating whether to simulate a spatially-explicit occupancy model with a Gaussian process. By default set to FALSE.
svc.cols: a vector indicating the variables whose effects will be estimated as spatially-varying coefficients. svc.cols is an integer vector with values indicating the order of covariates specified in the model formula (with 1 being the intercept if specified).
cov.model: a quoted keyword that specifies the covariance function used to model the spatial dependence structure among the latent occurrence values. Supported covariance model key words are: "exponential", "matern", "spherical", and "gaussian".
sigma.sq: a numeric value indicating the spatial variance parameter. Ignored when sp = FALSE.
phi: a numeric value indicating the spatial decay parameter. Ignored when sp = FALSE.
nu: a numeric value indicating the spatial smoothness parameter. Only used when sp = TRUE and cov.model = "matern".
x.positive: a logical value indicating whether the simulated covariates should be simulated as random standard normal covariates (x.positive = FALSE) or restricted to positive values using a uniform distribution with lower bound 0 and upper bound 1 (x.positive = TRUE).
grid: an atomic vector used to specify the grid across which to simulate the latent spatial processes. This argument is used to simulate the underlying spatial processes at a different resolution than the coordinates (e.g., if coordinates are distributed across a grid).
...: currently no additional arguments

Author

Jeffrey W. Doser doserjef@msu.edu,
Andrew O. Finley finleya@msu.edu

Value

A list comprised of:

X: a \(J \times p.occ\) numeric design matrix for the occupancy portion of the model.
X.p: a three-dimensional numeric array with dimensions corresponding to sites, repeat visits, and number of detection regression coefficients. This is the design matrix used for the detection portion of the occupancy model.
coords: a \(J \times 2\) numeric matrix of coordinates of each occupancy site. Required for spatial models.
w: a matrix of the spatial random effect values for each site. The number of columns is determined by the svc.cols argument (the number of spatially-varying coefficients).
psi: a \(J \times 1\) matrix of the occupancy probabilities for each site.
z: a length \(J\) vector of the latent occupancy states at each site.
p: a J x max(n.rep) matrix of the detection probabilities for each site and replicate combination. Sites with fewer than max(n.rep) replicates will contain NA values.
y: a J x max(n.rep) matrix of the raw detection-nondetection data for each site and replicate combination.
X.p.re: a three-dimensional numeric array containing the levels of any detection random effect included in the model. Only relevant when detection random effects are specified in p.RE.
X.re: a numeric matrix containing the levels of any occurrence random effect included in the model. Only relevant when occurrence random effects are specified in psi.RE.
alpha.star: a numeric vector that contains the simulated detection random effects for each given level of the random effects included in the detection model. Only relevant when detection random effects are included in the model.
beta.star: a numeric vector that contains the simulated occurrence random effects for each given level of the random effects included in the occurrence model. Only relevant when occurrence random effects are included in the model.

Examples

set.seed(400)
J.x <- 10
J.y <- 10
n.rep <- rep(4, J.x * J.y)
beta <- c(0.5, -0.15)
alpha <- c(0.7, 0.4)
phi <- 3 / .6
sigma.sq <- 2
psi.RE <- list(levels = 10, 
               sigma.sq.psi = 1.2)
p.RE <- list(levels = 15, 
             sigma.sq.p = 0.8)
dat <- simOcc(J.x = J.x, J.y = J.y, n.rep = n.rep, beta = beta, alpha = alpha,
              psi.RE = psi.RE, p.RE = p.RE, sp = TRUE, cov.model = 'spherical', 
              sigma.sq = sigma.sq, phi = phi)