| twoAFC {sensR} | R Documentation |
Creates af copy of the binomial family with the inverse link function changed to equal the 2-AFC psychometric function and correspondingly changed link function and derivative of the inverse link function.
twoAFC()
A binomial family object for models. Among other things it inludes the
psychometric function as
linkinv and the inverse psychometric function (for direct
dprime computation) as
linkfun.
Several functions in this package makes use of the function, but it may also be used on its own—see the example below.
Rune Haubo B Christensen and Per Bruun Brockhoff
Brockhoff, P.B. and Christensen, R.H.B.(2008). Thurstonian models for sensory discrimination tests as generalized linear models. Manuscript for Food Quality and Preference.
triangle, threeAFC,
duotrio, discrim,
discrimPwr, discrimSim,
AnotA, discrimSS,
samediff, findcr
xt <- matrix(c(10, 5), ncol = 2) ## data: 10 correct answers, 5 incorrect
res <- glm(xt ~ 1, family = twoAFC)
summary(res)
## Extended example plotting the profile likelihood
## data: 10 correct and 8 incorrect:
xt <- matrix(c(10, 8), ncol = 2)
summary(res <- glm(xt ~ 1, family = twoAFC))
N <- 100
dev <- double(N)
level <- c(0.95, 0.99)
delta <- seq(1e-4, 3, length = N)
for(i in 1:N)
dev[i] <- glm(xt ~ -1 + offset(delta[i]),
family = twoAFC)$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:
lim <- sapply(level, function(x)
exp(-qchisq(x, df=1)/2) )
abline(h = lim, col = "grey")