CDM (version 1.4-16)

sim.gdina: Simulation of the GDINA model

Description

The function sim.gdina.prepare creates necessary design matrices Mj, Aj and necc.attr. In most cases, only the list of item parameters delta must be modified by the user when applying the simulation function sim.gdina. The distribution of latent classes $\alpha$ is represented by an underlying multivariate normal distribution $\alpha^\ast$ for which a mean vector thresh.alpha and a covariance matrix cov.alpha must be specified. Alternatively, a matrix of skill classes alpha can be given as an input.

Usage

sim.gdina(n, q.matrix, delta, link = "identity", 
    thresh.alpha=NULL, cov.alpha=NULL, alpha=NULL,
    Mj, Aj, necc.attr)
sim.gdina.prepare( q.matrix )

Arguments

n

Number of persons

q.matrix

Q matrix

delta

List with $J$ entries where $J$ is the number of items. Every list element corresponds to the parameter of an item.

link

Link function. Choices are identity (default), logit and log.

thresh.alpha

Vector of thresholds (means) of $\alpha^\ast$

cov.alpha

Covariance matrix of $\alpha^\ast$

alpha

Matrix of skill classes if they should not be simulated

Mj

Design matrix, see gdina

Aj

Design matrix, see gdina

necc.attr

List with $J$ entries containing necessary attributes for each item

Value

• The output of sim.gdina is a list with following entries:
• data
  Simulated item responses
• alpha
  Data frame with simulated attributes
• q.matrix
  Used Q matrix
• delta
  Used delta item parameters
• Aj
  Design matrices Aj
• Mj
  Design matrices Mj
• link
  Used link function
• The function sim.gdina.prepare possesses the following values as output in a list: delta, necc.attr, Aj and Mj.

References

de la Torre, J. (2011) The generalized {DINA} model framework. Psychometrika, 76, 179--199.

See Also

For estimating the GDINA model see gdina.

Examples

##############################################
# Example: Simulating the GDINA model

n <- 50             # number of persons
# define Q matrix
q.matrix <- matrix(  c(1,1,0 ,
                0,1,1,
                1,0,1,
                1,0,0,
                0,0,1,
                0,1,0,
                1,1,1,
                0,1,1,
                0,1,1) , ncol=3 , byrow=TRUE)
# thresholds for attributes alpha^\ast
thresh.alpha <- c( .65 , 0 , -.30 )
# covariance matrix for alpha^\ast
cov.alpha <- matrix(1,3,3)
cov.alpha[1,2] <- cov.alpha[2,1] <- .4
cov.alpha[1,3] <- cov.alpha[3,1] <- .6
cov.alpha[3,2] <- cov.alpha[2,3] <- .8

# prepare design matrix by applying sim.gdina.prepare function
rp <- sim.gdina.prepare( q.matrix )
delta <- rp$delta
necc.attr <- rp$necc.attr
Aj <- rp$Aj
Mj <- rp$Mj
# define delta parameters
# intercept - main effects - second order interactions - ...
str(delta)  # => modify the delta parameter list which contains only zeroes as default
##   List of 9
##    $ : num [1:4] 0 0 0 0
##    $ : num [1:4] 0 0 0 0
##    $ : num [1:4] 0 0 0 0
##    $ : num [1:2] 0 0
##    $ : num [1:2] 0 0
##    $ : num [1:2] 0 0
##    $ : num [1:8] 0 0 0 0 0 0 0 0
##    $ : num [1:4] 0 0 0 0
##    $ : num [1:4] 0 0 0 0
delta[[1]] <- c( .2 , .1 , .15 , .4 )
delta[[2]] <- c( .2 , .3 , .3 , -.2 )
delta[[3]] <- c( .2 , .2 , .2 , 0 )
delta[[4]] <- c( .15 , .6 )
delta[[5]] <- c( .1 , .7 )
delta[[6]] <- c( .25 , .65 )
delta[[7]] <- c( .25 , .1 , .1 , .1 , 0 , 0 , 0 , .25 )
delta[[8]] <- c( .2 , 0 , .3 , -.1 )
delta[[9]] <- c( .2 , .2 , 0 , .3 )

#******************************************
# Now, the "real simulation" is starting
sim.res <- sim.gdina( n=n , q.matrix =q.matrix , delta=delta , link = "identity" , 
            thresh.alpha=thresh.alpha , cov.alpha=cov.alpha ,
                Mj=Mj , Aj=Aj , necc.attr =necc.attr)
# sim.res$data      # data
# sim.res$alpha     # alpha