Description Usage Value Note Author(s) References See Also Examples

Creates a binomial family object with the inverse link function equal to the psychometric function for the unspecified method of tetrads.

1 | ```
tetrad()
``` |

A binomial family object for models. Among other things it inludes the
psychometric function as
`linkinv`

and the inverse psychometric function (for direct
d-prime computation) as
`linkfun`

.

Several functions in this package makes use of functions in the tetrad family object, but it may also be used on its own—see the example below.

Rune Haubo B Christensen

Ennis, J. M., Ennis, D. M., Yip, D., & O'Mahony, M. (1998). Thurstonian models for variants of the method of tetrads. British Journal of Mathematical and Statistical Psychology, 51, pp. 205-215.

Ennis, J. M., & Jesionka, V. (2011). The power of sensory discrimination methods revisited. Journal of Sensory Studies, 26, pp. 371-382.

`duotrio`

, `twoAFC`

,
`threeAFC`

, `discrim`

,
`discrimPwr`

, `discrimSim`

,
`AnotA`

, `discrimSS`

,
`samediff`

, `findcr`

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 28 | ```
## Estimating d-prime using glm for a Tetrad test:
xt <- matrix(c(10, 5), ncol = 2) ## data: 10 correct answers, 5 incorrect
res <- glm(xt ~ 1, family = tetrad)
summary(res)
## Equivalent to (Estimate and Std. Error):
discrim(10, 15, method="tetrad")
## Extended example plotting the profile likelihood
## data: 10 correct answers, 9 incorrect
xt <- matrix(c(10, 9), ncol = 2)
summary(res <- glm(xt ~ 1, family = tetrad))
N <- 100
dev <- double(N)
delta <- seq(1e-4, 3, length = N)
for(i in 1:N)
dev[i] <- glm(xt ~ -1 + offset(delta[i]),
family = tetrad)$deviance
plot(delta, exp(-dev/2), type = "l",
xlab = expression(delta),
ylab = "Normalized Profile Likelihood")
## Add Normal approximation:
lines(delta, exp(-(delta - coef(res))^2 /
(2 * vcov(res))), lty = 2)
## Add confidence limits:
level <- c(0.95, 0.99)
lim <- sapply(level, function(x) exp(-qchisq(x, df=1)/2) )
abline(h = lim, col = "grey")
``` |

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