eDNAjoint (version 0.3.3)

traditional_model: Specify and fit model using count data from traditional, non eDNA surveys

Description

This function implements a Bayesian model that estimates expected species catch rate using count data from traditional, non eDNA surveys. When multiple traditional gear types are used, an optional variation allows estimation of gear scaling coefficients, which scale the catchability of gear types relative to the expected catch rate of a reference gear type. Model is implemented using Bayesian inference using the rstan package, which uses Hamiltonian Monte Carlo to simulate the posterior distributions. See more examples in the Package Vignette.

Usage

traditional_model(
  data,
  family = "poisson",
  q = FALSE,
  phi_priors = NULL,
  multicore = FALSE,
  initial_values = NULL,
  n_chain = 4,
  n_warmup = 500,
  n_iter = 3000,
  thin = 1,
  adapt_delta = 0.9,
  verbose = TRUE,
  seed = NULL
)

Value

A list of:

• a model object of class stanfit returned by rstan::sampling

• initial values used in MCMC

Arguments

data

A list containing data necessary for model fitting. Valid tags are count and count_type. count is a matrix or data frame of traditional survey count data, with first dimension equal to the number of sites (i) and second dimension equal to the maximum number of traditional survey replicates at a given site (j). count_type is an optional matrix or data frame of integers indicating gear type (k) used in corresponding count data, with first dimension equal to the number of sites (i) and second dimension equal to the maximum number of traditional survey replicates at a given site (j). Values should be integers beginning with 1 (referring to the first gear type) to n (last gear type). Empty cells should be NA and will be removed during processing. Sites, i, should be consistent in all count data.

family

The distribution class used to model traditional survey count data. Options include poisson ('poisson'), negative binomial ('negbin'), and gamma ('gamma'). Default value is 'poisson'.

q

A logical value indicating whether to estimate gear scaling coefficients, q, for traditional survey gear types (TRUE) or to not estimate gear scaling coefficients, q, for traditional survey gear types (FALSE). Default value is FALSE.

phi_priors

A numeric vector indicating gamma distribution hyperparameters (shape, rate) used as the prior distribution for phi, the overdispersion in the negative binomial distribution for traditional survey gear data. Used when family = 'negbin.' If family = 'negbin', then default vector is c(0.25,0.25), otherwise, default is NULL.

multicore

A logical value indicating whether to parallelize chains with multiple cores. Default is FALSE.

initial_values

A list of lists of initial values to use in MCMC. The length should equal the number of MCMC chains. Initial values can be provided for parameters: mu and q. If no initial values are provided, default random values are drawn.

n_chain

Number of MCMC chains. Default value is 4.

n_warmup

A positive integer specifying the number of warm-up MCMC iterations. Default value is 500.

n_iter

A positive integer specifying the number of iterations for each chain (including warmup). Default value is 3000.

thin

A positive integer specifying the period for saving samples. Default value is 1.

adapt_delta

Numeric value between 0 and 1 indicating target average acceptance probability used in rstan::sampling. Default value is 0.9.

verbose

Logical value controlling the verbosity of output (i.e., warnings, messages, progress bar). Default is TRUE.

seed

A positive integer seed used for random number generation in MCMC. Default is NULL, which means the seed is generated from 1 to the maximum integer supported by R.

Examples

# \donttest{
# Load data
data(green_crab_data)

# Examine data in list
# This function uses only traditional survey count data and optionally
# the count type data
names(green_crab_data)

# Note that the surveyed sites (rows) should match in the data
dim(green_crab_data$count)[1]
dim(green_crab_data$count_type)[1]

# Fit a model without estimating a gear scaling coefficient for traditional
# survey gear types.
# This model assumes all traditional survey methods have the same
# catchability.
# Count data is modeled using a poisson distribution.
fit_no_q <- traditional_model(data = green_crab_data, family = "poisson",
                              q = FALSE, phi_priors = NULL,
                              multicore = FALSE, verbose = TRUE)


# Fit a model estimating a gear scaling coefficient for traditional survey
# gear types.
# This model does not assume all traditional survey methods have the same
# catchability.
# Count data is modeled using a negative binomial distribution.
fit_q <- traditional_model(data = green_crab_data, family = "negbin",
                           q = TRUE, phi_priors = c(0.25,0.25),
                           multicore = FALSE, initial_values = NULL,
                           n_chain = 4, n_warmup = 500, n_iter = 3000,
                           thin = 1, adapt_delta = 0.9, verbose = TRUE,
                           seed = 123)
# }