Description Usage Arguments Details Value Author(s) References See Also Examples
Fits the Thurstonian DegreeofDifference (DOD) model and performs hypothesis/significance tests of dprime (Thurstonian delta). Onesided difference and similarity tests as well as twosided tests of dprime are available. The user may choose from a number of tests statistics.
1 2 3 4 5 6 7 
same 
the answers to samepairs; 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 differentpairs in the same format as

d.prime0 
the value of d.prime under the null hypothesis. In the
standard nodifference test 
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 dprime. Note that

control 
options to control the fitting process specfied via a
call to 
x 
an object of class 
digits 
number of digits in resulting table of results. 
... 
not currently used. 
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 pvalue for the standard onetailed difference test of "no
difference" is obtained with d.prime0 = 0
corresponding to the
default setting.
The standard error of dprime 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.
An object of class dod
.
Rune Haubo B Christensen
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.
dodSim
,
dodPwr
,
dodControl
, dod_fit
,
optimal_tau
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19  ## DOD example data:
same.pairs < c(25, 22, 33, 20)
diff.pairs < c(18, 22, 30, 30)
## Fit Thurstonian dodmodel and perform difference test:
dod(same=same.pairs, diff=diff.pairs)
## Can choose another test statistic (e.g. Wilcoxon):
dod(same=same.pairs, diff=diff.pairs, statistic="Wilcox")
## A similarity test (with simulated data):
set.seed(121)
(Data2 < dodSim(d.prime=0, ncat=4, sample.size=200, method.tau="equi.prob"))
dod(same=Data2[1, ], diff=Data2[2, ], d.prime0=1.2,
alternative="similarity")
## Extract parameters from a dod fit:
fm < dod(same=same.pairs, diff=diff.pairs)
coef(fm)

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