tune_proposals: Tune proposal densities

In duckmayr/bggum: Bayesian Estimation of Generalized Graded Unfolding Model Parameters

Description

Tunes the standard deviation for the parameters' proposal densities

Usage

tune_proposals(data, tune_iterations, K = NULL, thetas = NULL,
  alphas = NULL, deltas = NULL, taus = NULL,
  theta_prior_params = c(0, 1), alpha_prior_params = c(1.5, 1.5, 0.25,
  4), delta_prior_params = c(2, 2, -5, 5), tau_prior_params = c(2, 2,
  -6, 6))

Arguments

data	An integer matrix giving the response by each respondent to each item
tune_iterations	An integer vector of length one; the number of iterations to complete
K	(Optional) A numeric vector with an element for each item giving the number of options for the item; if not provided, it is generated by taking the number of unique options observed in the data
thetas	(Optional) A numeric vector giving an initial value for each respondent's theta parameter; if not given, the initial values are drawn from the prior distribution
alphas	(Optional) A numeric vector giving an initial value for each item's alpha parameter; if not given, the initial values are drawn from the prior distribution
deltas	(Optional) A numeric vector giving an initial value for each item's delta parameter; if not given, the initial values are drawn from the prior distribution
taus	(Optional) A list giving an initial value for each item's tau vector; if not given, the initial values are drawn from the prior distribution
theta_prior_params	A numeric vector of length two; the mean and standard deviation of theta parameters' prior distribution (where the theta parameters have a normal prior; the default is 0 and 1)
alpha_prior_params	A numeric vector of length four; the two shape parameters and a and b values for alpha parameters' prior distribution (where the alpha parameters have a four parameter beta prior; the default is 1.5, 1.5, 0.25, and 4)
delta_prior_params	A numeric vector of length four; the two shape parameters and a and b values for delta parameters' prior distribution (where the delta parameters have a four parameter beta prior; the default is 2, 2, -5, and 5)
tau_prior_params	A numeric vector of length four; the two shape parameters and a and b values for tau parameters' prior distribution (where the tau parameters have a four parameter beta prior; the default is 2, 2, -6, and 6)

Details

This function runs the MCMC algorithm for the number of iterations specified in tune_iterations, updating parameter values at each iteration. Every 100 iterations, the function determines how many of the previous 100 iterations resulted in an accepted proposal for each parameter. If the number of acceptances was less than 20, the standard deviation of the proposal for that parameter is decreased by (20 - N) * 0.01, where N is the number of acceptances in the previous 100 iterations. If N is greater than 25, the proposal standard deviation is increased by (N - 25) * 0.01.

Please see the vignette (via vignette("bggum")) for a full in-depth practical guide to Bayesian estimation of GGUM parameters.

Value

A list, where each element is a numeric vector; the first element is a numeric vector of standard deviations for the theta parameters' proposals, the second for the alpha parameters, the third for the delta parameters, and the fourth for the tau parameters

Warning

The parameters are updated in place; that is, if you supply objects for the theta, alpha, delta, and tau arguments, the objects will not hold the same values after the function is run (in the underlying C++ function, these objects are passed by reference).

Examples

## NOTE: This is a toy example just to demonstrate the function, which uses
## a small dataset and an unreasonably low number of tuning interations.
## For a longer practical guide on Bayesian estimation of GGUM parameters,
## please see the vignette ( via vignette("bggum") ).
## We'll simulate data to use for this example
set.seed(123)
sim_data <- ggum_simulation(100, 10, 2)
## Now we can tune the proposal densities
## (for the purposes of example, we use 100 iterations,
## though in practice you would use much more)
proposal_sds <- tune_proposals(data = sim_data$response_matrix,
                               tune_iterations = 100)

duckmayr/bggum documentation built on Jan. 20, 2020, 5:23 a.m.