# clm2twoAC: Extract 2-AC coefficient table from a cumulative link model In perbrock/sensR: Thurstonian Models for Sensory Discrimination

 clm2twoAC R Documentation

## Extract 2-AC coefficient table from a cumulative link model

### Description

The Thurstonian model for the 2-AC protocol can be formulated as a cumulative link model (see the references). This function extracts the 2-AC model parameter estimates, standard errors, z-value and p-values from a cumulative link (mixed) model fitted with `clm` or `clmm` from package `ordinal`.

### Usage

``````
clm2twoAC(object, ...)

``````

### Arguments

 `object` a `clm` or `clmm` object `...` not currently used.

### Value

A `data.frame` with the coefficient table. The two first rows contain the estimates of `tau` and `d.prime` while the remaining rows contain optional regression variables for `d.prime`.

### Author(s)

Rune Haubo B Christensen

### References

Christensen R.H.B., Lee H-S and Brockhoff P.B. (2012). Estimation of the Thurstonian model for the 2-AC protocol. Food Quality and Preference, 24(1), pp.119-128.

`twoAC`, `twoACpwr`

### Examples

``````
## Example of a simple 2-AC model. First the conventional way:
twoAC(c(2, 2, 6))

## The using a cumulative link model (clm from package ordinal):
if(require(ordinal)) {
response <- gl(3,1)
fit.clm <- clm(response ~ 1, weights = c(2, 2, 6), link = "probit")
clm2twoAC(fit.clm)
## Alternatively we could get estimates and standard errors "by hand":
tab <- coef(summary(fit.clm))
theta <- tab[,1]
(tau <- (theta[2] - theta[1])/sqrt(2))
(d.prime <- (-theta[2] - theta[1])/sqrt(2))
VCOV <- vcov(fit.clm)
(se.tau <- sqrt((VCOV[1,1] + VCOV[2,2] - 2*VCOV[2,1])/2))
(se.d.prime <- sqrt((VCOV[1,1] + VCOV[2,2] + 2*VCOV[2,1])/2))

## Extended example with a regression model for d.prime
## (see the referenced paper for details):
n.women <- c(2, 2, 6)*10
n.men <- c(1, 2, 7)*10
wt <- c(n.women, n.men)
response <- gl(3,1, length = 6)
gender <- gl(2, 3, labels = c("women", "men"))
fm2 <- clm(response ~ gender, weights = wt, link = "probit")
clm2twoAC(fm2)
}

``````

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