Epi: bootLexis – R documentation

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bootLexis

Create a bootstrap sample of persons (as identified by lex.id) from a Lexis object

Description

lex.id is the person identifier in a Lexis object. This is used to sample persons from a Lexis object. If a person is sampled, all records from this persons is transported to the bootstrap sample.

Usage

nid( Lx, ... )
## S3 method for class 'Lexis'
nid( Lx, by=NULL, ... )
bootLexis( Lx, size = NULL, by = NULL, replace=TRUE )

Arguments

`Lx`	A `Lexis` object.
`...`	Parameters passed on to other methods.
`size`	Numeric. How many persons should be sampled from the `Lexis` object. Defaults to the number of persons in the `Lx`, or, if `by` is given, to the number of persons in each level of `by`. If `by` is given, `size` can have length `length(unique(by))`, to indicate how many are sampled from each level of `by`.
`by`	Character. Name of a variable (converted to factor) in the `Lexis` object. Bootstrap sampling is done within each level of by. Calculation of the number of persons (`lex.id`) is done within each level of `by`, and a vector returned.
`replace`	Should persons be sampled by replacement? Default is `TRUE`. Setting `replace` to `FALSE` enables selecting a random subset of persons from the Lexis object.

Value

bootLexis returns a Lexis object of the same structure as the input, with persons bootstrapped. The variable lex.id in the resulting Lexis object has values 1,2,... The original values of lex.id from Lx are stored in the variable old.id.

nid counts the number of persons in a Lexis object, possibly by by. If by is given, a named vector is returned.

Author(s)

Bendix Carstensen, http://bendixcarstensen.com.

Examples

# A small bogus cohort
xcoh <- data.frame( id = c("A", "B", "C"),
                 birth = c("1952-07-14", "1954-04-01", "1987-06-10"),
                 entry = c("1965-08-04", "1972-09-08", "1991-12-23"),
                  exit = c("1997-06-27", "1995-05-23", "1998-07-24"),
                  fail = c(1, 0, 1),
                   sex = c("M","F","M") )
# Convert to calendar years
for( i in 2:4 ) xcoh[,i] <- cal.yr(xcoh[,i])
xcoh
Lcoh <- Lexis( entry = list( per=entry ),
                exit = list( per=exit, age=exit-birth ),
         exit.status = fail,
                data = xcoh )
Lx <- Lcoh[sample(1:3,10,replace=TRUE),]
Lx$per <- Lx$per + runif(10,0,10)
Lx$lex.id <- 1:10
Lx <- splitLexis( Lx, breaks=0:10*10, "age" )
Lx
nid( Lx )
nid( Lx, by="sex" )
Lb <- bootLexis( Lx )
head( Lb )
nid( bootLexis( Lx, size=7 ) )
Li <- bootLexis( Lx, by="id" ) # superfluous
summary( Lx )
summary( Li )
L2 <- bootLexis( Lx, by="sex", size=c(2,5) )
nid( L2, by="sex" )
summary( L2 )

Epi

Statistical Analysis in Epidemiology

v2.44

GPL-2

Authors

Bendix Carstensen [aut, cre], Martyn Plummer [aut], Esa Laara [ctb], Michael Hills [ctb]

Initial release

2021-02-28