Description Usage Arguments Details Value Author(s) References Examples
Calculates the percentiles of a numeric variable in an
edsurvey.data.frame
, a light.edsurvey.data.frame
,
or an edsurvey.data.frame.list
.
1 2 3 4 
variable 
the character name of the variable to percentiles computed, typically a subject scale or subscale 
percentiles 
a numeric vector of percentiles in the range 0 to 100 (inclusive) 
data 
an 
weightVar 
a character indicating the weight variable to use. (See Details.) 
jrrIMax 
a numeric value; when using the jackknife variance estimation method, the default estimation option, 
varMethod 
a character set to 
alpha 
a numeric value between 0 and 1 indicating the confidence level.
An 
omittedLevels 
a logical value. When set to the default value of

defaultConditions 
a logical value. When set to the default value
of 
recode 
a list of lists to recode variables. Defaults to

returnVarEstInputs 
a logical value set to 
returnNumberOfPSU 
a logical value set to 
Percentiles, their standard errors, and confidence intervals are calculated according to the vignette titled Methods Used for Estimating Percentiles. Note that the standard errors and confidence intervals are based on separate formulas and assumptions.
The Taylor series variance estimation procedure is not relevant to percentiles because percentiles are not continuously differentiable.
The return type depends on whether the class of the data
argument is an
edsurvey.data.frame
or an edsurvey.data.frame.list
.
When the data
argument is an edsurvey.data.frame
,
percentile
returns an S3 object of class percentile
.
This is a data.frame
with typical attributes (names
,
row.names
, and class
) and additional attributes as follows:
number of rows on edsurvey.data.frame
before any conditions were applied
number of observations with valid data and weights larger than zero
number of PSUs used in calculation
the call used to generate these results
The columns of the data.frame
are as follows:
the percentile of this row
the estimated value of the percentile
the jackknife standard error of the estimated percentile
degrees of freedom
the lower bound of the confidence interval
the upper bound of the confidence interval
number of units with more extreme results, averaged across plausible values
When the data
argument is an edsurvey.data.frame.list
,
percentile
returns an S3 object of class percentileList
.
This is a data.frame with a call
attribute.
The columns in the data.frame
are identical to those in the previous
section, but there also are columns from the edsurvey.data.frame.list
.
a column for each column in the covs
value of the
edsurvey.data.frame.list
.
See Examples.
When returnVarEstInputs
is TRUE
, an attribute
varEstInputs
also is returned that includes the variance estimate
inputs used for calculating covariances with varEstToCov
.
Paul Bailey
Hyndman, R. J., & Fan, Y. (1996). Sample quantiles in statistical packages. American Statistician, 50, 361–365.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27  # read in the example data (generated, not real student data)
sdf < readNAEP(system.file("extdata/data", "M36NT2PM.dat", package="NAEPprimer"))
# get the median of the composite
percentile("composite", 50, sdf)
# get several percentiles
percentile("composite", c(0,1,25,50,75,99,100), sdf)
## Not run:
# build an edsurvey.data.frame.list
sdfA < subset(sdf, scrpsu %in% c(5,45,56))
sdfB < subset(sdf, scrpsu %in% c(75,76,78))
sdfC < subset(sdf, scrpsu %in% 100:200)
sdfD < subset(sdf, scrpsu %in% 201:300)
sdfl < edsurvey.data.frame.list(list(sdfA, sdfB, sdfC, sdfD),
labels=c("A locations",
"B locations",
"C locations",
"D locations"))
# this shows how these datasets will be described:
sdfl$covs
percentile("composite", 50, sdfl)
percentile("composite", c(25, 50, 75), sdfl)
## End(Not run)

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