twoAC: 2-AC Discrimination and Preference Protocol In sensR: Thurstonian Models for Sensory Discrimination

Description

Computes estimates and standard errors of d-prime and tau for the two alternative (2-AC) protocol. A confidence interval and significance test for d-prime is also provided. The 2-AC protocol is equivalent to a 2-AFC protocol with a "no-difference" option, and equivalent to a paired preference test with an "no-preference" option.

Usage

 1 2 3 twoAC(data, d.prime0 = 0, conf.level = 0.95, statistic = c("likelihood", "Wald"), alternative = c("two.sided", "less", "greater"), ...)

Arguments

 data a non-negative numeric vector of length 3 with the number of observations in the three response categories in the form ("prefer A", "no-preference", "prefer B"). If the third element is larger than the first element, the estimate of d-prime is positive. d.prime0 the value of d-prime under the null hypothesis for the significance test. conf.level the confidence level. statistic the statistic to use for confidence level and significance test. alternative the type of alternative hypothesis. ... not currently used.

Details

confint, profile, logLik, vcov, and print methods are implemented for twoAC objects.

Power computations for the 2-AC protocol is implemented in twoACpwr.

Value

An object of class twoAC with elements

 coefficients 2 by 2 coefficient matrix with estimates and standard errors of d-prime and tau. If the variance-covariance matrix of the parameters is not defined, the standard errors are NA. vcov variance-covariance matrix of the parameter estimates. Only present if defined for the supplied data. data the data supplied to the function. call the matched call. logLik the value of the log-likelihood at the maximum likelihood estimates. alternative the name of the alternative hypothesis for the significance test. statistic the name of the test statistic used for the significance test. conf.level the confidence level for the confidence interval for d-prime. d.prime0 the value of d-prime under the null hypothesis in the significance test. p.value p-value of the significance test. confint two-sided condfidence interval for d-prime. This is only available if the standard errors are defined, which may happen in boundary cases. Use profile and confint methods to get confidence intervals instead; see the examples.

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.