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

## 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

 `1` ```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. (2011). Estimation of the Thurstonian model for the 2-AC protocol. Submitted to Food Quality and Preference.

`twoAC`, `twoACpwr`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27``` ```## 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 - theta)/sqrt(2)) (d.prime <- (-theta - theta)/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) } ```