dod: Thurstonian Degree-of-Difference (DOD) model In sensR: Thurstonian Models for Sensory Discrimination

Description

Fits the Thurstonian Degree-of-Difference (DOD) model and performs hypothesis/significance tests of d-prime (Thurstonian delta). One-sided difference and similarity tests as well as two-sided tests of d-prime are available. The user may choose from a number of tests statistics.

Usage

 1 2 3 4 5 6 7 dod(same, diff, d.prime0 = 0, conf.level = 0.95, statistic = c("likelihood", "Pearson", "Wilcoxon", "Wald"), alternative = c("difference", "similarity", "two.sided", "less", "greater"), control=dodControl(), ...) ## S3 method for class 'dod' print(x, digits = max(3, getOption("digits") - 3), ...)

Arguments

 same the answers to same-pairs; either 1) a numeric vector of counts of length equal to the number of response categories ordered appropriately or 2) a factor where the levels indicate the response categories. diff the answers to different-pairs in the same format as same. d.prime0 the value of d.prime under the null hypothesis. In the standard no-difference test d.prime0 = 0, while it has to be positive for similarity tests and two-sided tests. conf.level the confidence level for the confidence intervals statistic the statistic to be used for hypothesis testing alternative the nature of the alternative hypothesis in the hypothesis/significance test for d-prime. Note that "greater" is an alias for "difference" and "less" is an alias for "similarity" control options to control the fitting process specfied via a call to dodControl. x an object of class "dod". digits number of digits in resulting table of results. ... not currently used.

Details

dod will report the likelihood based confidence interval for d.prime unless statistic = "Wald" in which case the standard symmetric Wald type confidence interval is reported. This interval can be highly inaccurate and so is not recommened for practical use.

The p-value for the standard one-tailed difference test of "no difference" is obtained with d.prime0 = 0 corresponding to the default setting.

The standard error of d-prime is not defined when the parameter estimate is zero (or numerically close) and it will be reported as NA in this case.

The "Wald" statistic is *NOT* recommended for practical use—it is only included here for completeness and to allow comparisons with other software etc.

Value

An object of class dod.

Author(s)

Rune Haubo B Christensen

References

Ennis, J.M. and R.H.B. Christensen (2014) A Thurstonian comparison of the tetrad and degree of difference tests. Food Quality and Preference, in press.

Christensen, R.H.B, J.M. Ennis, D.M. Ennis and P.B Brockhoff (2012) A Thurstonian model for the Degree of Difference test with extensions to unequal variance, sequence effects and replicated data. Talk at Sensometrics conference, Rennes, France, July 11th.