anchors {anchors}  R Documentation 
Nonparametric analysis of surveys with vignette anchors.
anchors(formula, data, method = c("B","C"), options=anchors.options(), subset, combn = FALSE, na.action = na.omit)
formula 
A list of named formulas giving a symbolic description of the model to be fit. See Details below. 
data 
A data frame or matrix. See Details below. 
method 
Single string indicating method of analysis. See Details below. 
options 
A list of class 'anchors.options', produced by function

subset 
Logical expression indicating elements or rows to keep:
missing values are taken as false; equivalent to function 
combn 
Logical (TRUE/FALSE). Calculate key statistics for all combinations of subsets of vignettes specified in formula=list(vign=cbind(...)) 
na.action 
Specify the "NA action" which should be applied to 'data'. Default is R standard option 'na.omit'; can also be set to 'na.fail'. 
The formula syntax is designed to allow the same list of formulas
to be used for both anchors and chopit.
If a user would like to use exactly the same cases with
chopit
as with anchors
(i.e., drop cases with any
missing responses or missing cpolr
values), and vise versa (i.e.,
also drop any case with missing values in the tau=
,
tau1=
formulae), then the user should use the same list of
formula for all methods and use the option
anchors.options(delete="maximal")
. See example below.
Only options relevant to anchors
are discussed here.
The named list() of formulas may include
self: LHS selfresponse variable; RHS is simply 1 (needed to define a formula); actually anything can be put on the RHS, and it will not by default be used.
vign: vignette responses, bound together by cbind (as in glm binomial syntax), with ONLY '~ 1' as RHS of equation (formulas must have RHS).
cpolr: OPTIONAL. linear predictors used by the censored ordered
probit, cpolr
, model to
break ties in
rank based models, method="B" or "C". Default is cpolr = ~ 1 (i.e.,
an intercept only).
Example:
fo < list(self = xsayself ~ 1, vign = cbind(xsay3,xsay1) ~ 1, cpolr = ~ age )
NOTE: one can also use a single formula as a short hand: specifying
fo < self ~ vign1 + vign2
is equivalent to
fo < list(self = self ~ 1 vign = cbind(vign1,vign2) ~ 1, cpolr= ~ 1)
All of the response variables must be in the form of consequetive nonnegative numeric integers, i.e., 1, 2, ... K.
** anchors
currently does not support factor responses.**
The method="B" and "C" requires that cases with any response
that is missing be dropped. Any cases with missing values
the covariates specified in the cpolr=
formula are also
dropped. BUT by default these methods ignore missing values in the
covariates specified by tau=
, tau1=
, or the right hand
side of self=
.
Specific values listed below are meant for programmers; data analysts
should see the values produced by the summary.anchors
function.
rank 
List object containing:

summary 
list of summary statistics about ranks 
minentropy 
Matrix specifying how interval rank values would be allocated to scalar rank values to minimize entropy. 
cpolr 
a 
type 
The type of nonparamtric analysis (B or C) 
Related materials and worked examples are available at http://wand.stanford.edu/anchors/
Jonathan Wand http://wand.stanford.edu
Wand, Jonathan; Gary King; and Olivia Lau. (2007) “Anchors: Software for Anchoring Vignettes”. Journal of Statistical Software. Forthcoming. copy at http://wand.stanford.edu/research/anchorsjss.pdf
Wand, Jonathan. (2007) "Credible Comparisons Using Interpersonally Incomparable Data: Ranking selfevaluations relative to anchoring vignettes or other common survey questions". copy at http://wand.stanford.edu/anchors/wand_anchors.pdf
Wand, Jonathan and Gary King. (2007) Anchoring Vignetttes in R: A (different kind of) Vignette copy at http://wand.stanford.edu/anchors/doc/anchors.pdf
Gary King and Jonathan Wand. "Comparing Incomparable Survey Responses: New Tools for Anchoring Vignettes," Political Analysis, 15, 1 (Winter, 2007): Pp. 4666, copy at http://gking.harvard.edu/files/abs/cabs.shtml.
King, Gary; Christopher J.L. Murray; Joshua A. Salomon; and Ajay Tandon. "Enhancing the Validity and Crosscultural Comparability of Survey Research," American Political Science Review, Vol. 98, No. 1 (February, 2004): 191207, copy at http://gking.harvard.edu/files/abs/vignabs.shtml
anchors.order
,
anchors.options
,
chopit
,
data(mexchn) fo < list(self = xsayself ~ age, vign = cbind(xsay3,xsay1) ~ 1, tau = ~ age + china, tau1 = ~ age + china + male, cpolr= ~ china + male ) a2 < anchors(fo, data = mexchn, method="B") summary(a2) a3 < anchors(fo, data = mexchn, method="C") summary(a3)