gmultmix: Generalized multinomial-mixture model

Description

A three level hierarchical model for designs involving repeated counts that yield multinomial outcomes. Possible data collection methods include repeated removal sampling and double observer sampling. The three model parameters are abundance, availability, and detection probability.

Usage

gmultmix(lambdaformula, phiformula, pformula, data, mixture = c("P", "NB"), K, 
    starts, method = "BFGS", control = list(), se = TRUE)

Arguments

lambdaformula

Righthand side (RHS) formula describing abundance covariates

phiformula

RHS formula describing availability covariates

pformula

RHS formula describing detection covariates

data

An object of class unmarkedFrameGMM

mixture

Either "P" or "NB" for Poisson and Negative Binomial mixing distributions.

The upper bound of integration

starts

Starting values

method

Optimization method used by optim

control

List of control arguments passed to optim

Logical. Should standard errors be calculated?

Value

An object of class unmarkedFitGMM.

Details

The latent transect-level super-population abundance distribution $f(M | \mathbf{\theta})$ can be set as either a Poisson or a negative binomial random variable, depending on the setting of the mixture argument. mixture = "P" or mixture = "NB" select the Poisson or negative binomial distribution respectively. The mean of $M_i$ is $\lambda_i$. If $M_i \sim NB$, then an additional parameter, $\alpha$, describes dispersion (lower $\alpha$ implies higher variance). The number of individuals available for detection at time t is a modeled as binomial: $N_{it} \sim Binomial(M_i, \mathbf{\phi_ij})$. The detection process is modeled as multinomial: $y_{ij} \sim Multinomial(N_it, pi_{itj})$, where $pi_itj$ is the multinomial cell probability for plot i at time t on occasion j. Cell probabilities are computed via a user-defined function related to the sampling design. Alternatively, the default functions removalPiFun or doublePiFun can be used for equal-interval removal sampling or double observer sampling. Note that the function for computing cell probabilites is specified when setting up the data using unmarkedFrameGMM. Parameters $\lambda$, $\phi$ and $p$ can be modeled as linear functions of covariates using the log, logit and logit links respectively.

References

Royle, J. A. (2004) Generalized estimators of avian abundance from count survey data. Animal Biodiversity and Conservation 27, pp. 375--386. Chandler, R. B., J. A. Royle, and D. I. King. In Press. Inference about density and temporary emigration in unmarked populations. Ecology

Examples

Run this code

# Simulate data using the multinomial-Poisson model with a 
# repeated constant-interval removal design. 

n <- 100  # number of sites
T <- 4    # number of primary periods
J <- 3    # number of secondary periods

lam <- 3
phi <- 0.5
p <- 0.3

#set.seed(26)
y <- array(NA, c(n, T, J))
M <- rpois(n, lam)          # Local population size
N <- matrix(NA, n, T)       # Individuals available for detection
    
for(i in 1:n) {
    N[i,] <- rbinom(T, M[i], phi)
    y[i,,1] <- rbinom(T, N[i,], p)    # Observe some
    Nleft1 <- N[i,] - y[i,,1]         # Remove them
    y[i,,2] <- rbinom(T, Nleft1, p)   # ...
    Nleft2 <- Nleft1 - y[i,,2]
    y[i,,3] <- rbinom(T, Nleft2, p)
    }
    
y.ijt <- cbind(y[,1,], y[,2,], y[,3,], y[,4,])


umf1 <- unmarkedFrameGMM(y=y.ijt, numPrimary=T, type="removal")

(m1 <- gmultmix(~1, ~1, ~1, data=umf1, K=30))

backTransform(m1, type="lambda")        # Individuals per plot
backTransform(m1, type="phi")           # Probability of being avilable
(p <- backTransform(m1, type="det"))    # Probability of detection
p <- coef(p)

# Multinomial cell probabilities under removal design
c(p, (1-p) * p, (1-p)^2 * p)

# Or more generally:
head(getP(m1))

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