FUP: Estimate the coefficients of a filtered unconstrained...

In fungible: Psychometric Functions from the Waller Lab

Estimate the coefficients of a filtered unconstrained polynomial IRT model

Description

Estimate the coefficients of a filtered unconstrained polynomial IRT model.

Usage

FUP(data, thetaInit, item, startvals, k = 0)

Arguments

data	N(subjects)-by-p(items) matrix of 0/1 item response data.
thetaInit	Initial theta surrogates (e.g., calculated by svdNorm).
item	item number for coefficient estimation.
startvals	start values for function minimization.
k	order of monotonic polynomial = 2k+1 (see Liang & Browne, 2015).

Value

b	Vector of polynomial coefficients.
FHAT	Function value at convergence.
counts	Number of function evaluations during minimization (see optim documentation for further details).
AIC	Pseudo scaled Akaike Information Criterion (AIC). Candidate models that produce the smallest AIC suggest the optimal number of parameters given the sample size. Scaling is accomplished by dividing the non-scaled AIC by sample size.
BIC	Pseudo scaled Bayesian Information Criterion (BIC). Candidate models that produce the smallest BIC suggest the optimal number of parameters given the sample size. Scaling is accomplished by dividing the non-scaled BIC by sample size.
convergence	Convergence = 0 indicates that the optimization algorithm converged; convergence=1 indicates that the optimization failed to converge. .

Author(s)

Niels Waller

References

Liang, L. & Browne, M. W. (2015). A quasi-parametric method for fitting flexible item response functions. Journal of Educational and Behavioral Statistics, 40, 5–34.

Examples

## Not run: 
NSubjects <- 2000


## generate sample k=1 FMP data
b <- matrix(c(
    #b0    b1     b2    b3      b4   b5 b6 b7  k
  1.675, 1.974, -0.068, 0.053,  0,  0,  0,  0, 1,
  1.550, 1.805, -0.230, 0.032,  0,  0,  0,  0, 1,
  1.282, 1.063, -0.103, 0.003,  0,  0,  0,  0, 1,
  0.704, 1.376, -0.107, 0.040,  0,  0,  0,  0, 1,
  1.417, 1.413,  0.021, 0.000,  0,  0,  0,  0, 1,
 -0.008, 1.349, -0.195, 0.144,  0,  0,  0,  0, 1,
  0.512, 1.538, -0.089, 0.082,  0,  0,  0,  0, 1,
  0.122, 0.601, -0.082, 0.119,  0,  0,  0,  0, 1,
  1.801, 1.211,  0.015, 0.000,  0,  0,  0,  0, 1,
 -0.207, 1.191,  0.066, 0.033,  0,  0,  0,  0, 1,
 -0.215, 1.291, -0.087, 0.029,  0,  0,  0,  0, 1,
  0.259, 0.875,  0.177, 0.072,  0,  0,  0,  0, 1,
 -0.423, 0.942,  0.064, 0.094,  0,  0,  0,  0, 1,
  0.113, 0.795,  0.124, 0.110,  0,  0,  0,  0, 1,
  1.030, 1.525,  0.200, 0.076,  0,  0,  0,  0, 1,
  0.140, 1.209,  0.082, 0.148,  0,  0,  0,  0, 1,
  0.429, 1.480, -0.008, 0.061,  0,  0,  0,  0, 1,
  0.089, 0.785, -0.065, 0.018,  0,  0,  0,  0, 1,
 -0.516, 1.013,  0.016, 0.023,  0,  0,  0,  0, 1,
  0.143, 1.315, -0.011, 0.136,  0,  0,  0,  0, 1,
  0.347, 0.733, -0.121, 0.041,  0,  0,  0,  0, 1,
 -0.074, 0.869,  0.013, 0.026,  0,  0,  0,  0, 1,
  0.630, 1.484, -0.001, 0.000,  0,  0,  0,  0, 1), 
  nrow=23, ncol=9, byrow=TRUE)  
 
# generate data using the above item parameters 
ex1.data<-genFMPData(NSubj = NSubjects, bParams = b, seed = 345)$data

NItems <- ncol(ex1.data)

# compute (initial) surrogate theta values from 
# the normed left singular vector of the centered 
# data matrix
thetaInit <- svdNorm(ex1.data)

# Choose model
k <- 1  # order of polynomial = 2k+1

# Initialize matrices to hold output
if(k == 0) {
  startVals <- c(1.5, 1.5)
  bmat <- matrix(0,NItems,6)
  colnames(bmat) <- c(paste("b", 0:1, sep = ""),"FHAT", "AIC", "BIC", "convergence") 
}

if(k == 1) {
  startVals <- c(1.5, 1.5, .10, .10)
  bmat <- matrix(0,NItems,8)
  colnames(bmat) <- c(paste("b", 0:3, sep = ""),"FHAT", "AIC", "BIC", "convergence") 
}

if(k == 2) {
  startVals <- c(1.5, 1.5, .10, .10, .10, .10)
  bmat <- matrix(0,NItems,10)
  colnames(bmat) <- c(paste("b", 0:5, sep = ""),"FHAT", "AIC", "BIC", "convergence") 
}

if(k == 3) {
  startVals <- c(1.5, 1.5, .10, .10, .10, .10, .10, .10)
  bmat <- matrix(0,NItems,12)
  colnames(bmat) <- c(paste("b", 0:7, sep = ""),"FHAT", "AIC", "BIC", "convergence") 
}   


# estimate item parameters and fit statistics
for(i in 1:NItems){
  out<-FUP(data = ex1.data,thetaInit = thetaInit, item = i, startvals = startVals, k = k)
  Nb <- length(out$b)
  bmat[i,1:Nb] <- out$b
  bmat[i,Nb+1] <- out$FHAT
  bmat[i,Nb+2] <- out$AIC
  bmat[i,Nb+3] <- out$BIC
  bmat[i,Nb+4] <- out$convergence
}

# print results
print(bmat)

## End(Not run)

fungible documentation built on May 29, 2024, 8:28 a.m.