erf {FMP}

Utility fnc to compute the components for an empirical response function

Description

Utility function to compute empirical response functions.

Usage

 erf(theta, data, whichItem, min = -3, max = 3, Ncuts = 12)

Arguments

theta

Vector of estimated latent trait scores.

data

A matrix of binary item responses.

whichItem

Data for an erf will be generated for whichItem.

min

Default = -3. Minimum value of theta.

max

Default = 3. Maximum value of theta.

Ncuts

Number of score groups for erf.

Value

probs

A vector (of length Ncuts) of bin response probabilities for the empirical response function.

centers

A vector of bin centers.

Ni

Bin sample sizes.

se.p

Standard errors of the estimated bin response probabilities.

Author(s)

Niels Waller

Examples

NSubj <- 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)  
 
theta <- rnorm(NSubj)  
data<-genFMPData(NSubj = NSubj, bParam = b, theta = theta, seed = 345)$data

erfItem1 <- erf(theta, data, whichItem = 1, min = -3, max = 3, Ncuts = 12)

plot( erfItem1$centers, erfItem1$probs, type="b", 
      main="Empirical Response Function",
      xlab = expression(theta),
      ylab="Probability",
      cex.lab=1.5)