R: Batch EZ2 model fitting

EZ2batch {EZ2}

R Documentation

Batch EZ2 model fitting

Description

Fit the a simplified diffusion model for response time and accuracy in batch to each row of a data frame.

Usage

EZ2batch(pstart, ObsValPair, ..., data, nrestart = 1, method = "Nelder-Mead", control = list(), hessian = FALSE)

Arguments

`pstart`	Numeric vector with named elements. Starting point.
`ObsValPair`	Formula or list of formulas relating observed value(s) to parameters. See examples below.
`...`	More formulas.
`data`	Data frame with observed values.
`nrestart`	Number of times the fitting should restarted. Defaults to 1.
`method`	See `method` parameter of `optim`.
`control`	See `control` parameter of `optim`.
`hessian`	See `hessian` parameter of `optim`.

Details

The number of restarts needs to be increased if the model entails the same number of estimated parameters as the number of modeled moments and any of the values in the value column in the returned data frame is not close to 1.0e-08.

An important bug to note: for EZbatch to fit the rows in the provided data.frame there should be no variables in the global environment with the same name as the column names of the data.frame.

Value

Data frame with parameter estimates and convergence information.

Author(s)

Raoul Grasman

References

Grasman, Wagenmakers, and van der Maas (2008) EZ2: An extention of the EZ-diffusion model for Response Time and Accuracy, Manuscript submitted for publication in J. Math. Psych.

Examples

## create some data (theoretical values, not simulated)
## create some data (theoretical values, not simulated) Needless to say, in reality you would like to fit real data!
A = seq(.08,.13,len=6)
X2 = data.frame(A=A)
X2$vrt0 = sapply(A, function(a) EZ2.vrt(.1,.05,a))
X2$pe0 = sapply(A, function(a) EZ2.pe(.1,.05,a))
X2$vrt1 = sapply(A, function(a) EZ2.vrt(.2,a-.05,a))
X2$pe1 = sapply(A, function(a) EZ2.pe(.2,a-.05,a))

X2 = as.data.frame(X2)          # now pretend that X2 is the data frame that you may have computed from real data

## fit an EZ2 model on each row
#  method 1:
EZ2batch(c(v0=.11,v1=.21,z=.05,a=.09), 
 vrt0 ~ EZ2.vrt(v0,z,a), 
  pe0 ~ EZ2.pe(v0,z,a), 
 vrt1 ~ EZ2.vrt(v1,a-z,a), 
  pe1 ~ EZ2.pe(v1, a-z, a), data=X2)

# method 2 (eventually less typing):
mdl <- list( vrt0 ~ EZ2.vrt(v0,z,a), 
              pe0 ~ EZ2.pe(v0,z,a), 
             vrt1 ~ EZ2.vrt(v1,a-z,a), 
              pe1 ~ EZ2.pe(v1, a-z, a)
           )
EZ2batch(c(v0=.11,v1=.21,z=.05,a=.09), mdl, data=X2)

[Package EZ2 version 1.0 Index]