# dod_fit: Direct fitter of the Thurstonian Degree-of-Difference (DOD)... In perbrock/sensR: Thurstonian Models for Sensory Discrimination

 dod_fit R Documentation

## Direct fitter of the Thurstonian Degree-of-Difference (DOD) model

### Description

Fits the Thurstonian Degree-of-Difference (DOD) model. This function is for programming use. The ordinary user probably wants the `dod` function, which is for interactive use. `dod_fit` only estimates the DOD model and performs no hypothesis or significance tests.

### Usage

``````
dod_fit(same, diff, tau=NULL, d.prime=NULL, control=dodControl(),
...)

``````

### Arguments

 `same` the answers to same-pairs; either 1) a numeric vector of counts of length equal to the number of response categories ordered appropriately or 2) a factor where the levels indicate the response categories. `diff` the answers to different-pairs in the same format as `same`. `tau` optional vector of boundary parameters. If specified, `dod_fit` will not optimize over the `tau` parameters. `d.prime` optional d-prime value. If specified, `dod_fit` will not optimize over `d.prime`. `control` options to control the fitting process specfied via a call to `dodControl`. `...` not currently used.

### Details

The standard error of d-prime is not defined when the parameter estimate is zero (or numerically close) and it will be reported as `NA` in this case.

### Value

An object of class `dod_fit`.

### Author(s)

Rune Haubo B Christensen

`dod`, `dodSim`, `optimal_tau`, `dodPwr`, `dodControl`

### Examples

``````
## DOD example data:
same.pairs <- c(25, 22, 33, 20)
diff.pairs <- c(18, 22, 30, 30)

## Fit Thurstonian dod-model and perform difference test:
fm <- dod_fit(same=same.pairs, diff=diff.pairs)
names(fm)

## Estimate d-prime for given tau:
fm <- dod_fit(same=same.pairs, diff=diff.pairs, tau=1:3)

## Estimate tau for given d-prime:
fm <- dod_fit(same=same.pairs, diff=diff.pairs, d.prime=1)

``````

perbrock/sensR documentation built on Nov. 5, 2023, 10:41 a.m.