The 'ilab' class.
Description
The ‘ilab’ class and its constructor function.
Usage
1 2 
Arguments
org 
Character vector or factor of organisation names. 
item 
vector or factor of identifiers for test items. Coerced to factor on storage. 
measurand 
vector or factor identifying the measurand(s) involved in the study. 
x 
numeric vector of reported values. 
u 
numeric vector of reported standard uncertainties or standard errors associated with x. 
df 
optional numeric vector of degrees of freedom associated with each reported uncertainty. 
k 
numeric vector of coverage factors. The coverage factor is the factor multiplying u to obtain U. 
U 
numeric or character vector of expanded uncertainties or confidence interval halfwidths. Coerced to numeric but may include a character representation of interval limits; see Details. 
U.lower, U.upper 
numeric vectors of lower and upper limits for the confidence interval around x, allowing asymmetric intervals. Defaults to U or to the limits specified by U. See Details. 
distrib 
A character vector of length 
distrib.pars 
A named list of lists of parameters describing the distributions
associated with 
study 
A character value or vector or a factor identifying different studies
or study populations within the data set. Typically used, for example, for identifying
participants in global and regional components of a combined study. Recycled to length

title 
An optional title for the study. May be a character vector, in which case each element is displayed on a separate line when printed. 
p 
Confidence level assumed to apply to 
... 
Other named factors or character vectors used to group observations. 
Details
If U
is a character vector, it may contain character representations of range.
Two forms are permitted:
 "ab"
Interpreted as limits of a range from
a
tob
.U.lower
andU.upper
are calculated from these limits andx
 "+a[/]b" (or "a[/]+b")
U.upper
is set toa
in"+a"
, andU.lower
is set tob
in"b"
.
If distrib.pars
is missing, an attempt is made to deduce appropriate
distribution parameters from x
, u
, df
and distrib
.
In doing so, the following assumptions and values apply for the respective distributions:
 norm
mean=x$name, sd=u$name
. unif
min=xsqrt(3)*u, max=x+sqrt(3)*u
. tri
min=xsqrt(6)*u, max=x+sqrt(6)*u, mode=x
. t, t.scaled
df=df, mean=x, sd=u
.
In addition, if distrib
contains "t"
or "t.scaled"
, and
df
is NA
, the corresponding degrees of freedom are chosen based on
k
and p
.
Value
An object of class ‘ilab’ consisting of:
title 
A character value or vector describing the study  
subset 
A character string describing any subset operation used to form the object.  
data 
A data frame with columns:
 
distrib 
An unnamed list of distribution names.  
distrib.pars 
An unnamed list of lists of parameters describing the distributions
associated with 
Author(s)
S. L. R. Ellison s.ellison@lgc.co.uk
References
None, yet.
See Also
print.ilab
, subset.ilab
, plot.ilab
Examples
1 2 3 4 5 6 7 8 9 10 11  data(Pb)
construct.ilab(org=Pb$lab, x=Pb$value, measurand="Pb", item="none",
u=Pb$u, k=Pb$k, U=Pb$U, title=c("CCQM K30", "Lead in wine"),
method=Pb$method)
#Illustrate default for U and automatic distrib.pars
construct.ilab(org=Pb$lab, x=Pb$value, measurand="Pb", item="none",
u=Pb$u, k=Pb$k, distrib="norm")
construct.ilab(org=Pb$lab, x=Pb$value, measurand="Pb", item="none",
u=Pb$u, k=Pb$k, distrib="t.scaled")
