Epi (version 1.1.20)

cutLexis: Cut follow-up at a specified date for each person.

Description

Follow-up intervals in a Lexis object are divided into two sub-intervals: one before and one after an intermediate event. The intermediate event may denote a change of state, in which case the entry and exit status variables in the split Lexis object are modified.

Usage

cutLexis <- function(data,
                     cut,
                     timescale = 1,
                     new.state = nlevels(data$lex.Cst)+1,
                     new.scale = FALSE,
                     split.states = FALSE,
                     progressive = FALSE,
                     precursor.states = NULL,
                     count = FALSE)
  countLexis(data, cut, timescale = 1)

Arguments

data

A Lexis object.

cut

A numeric vector with the times of the intermediate event. If a time is missing (NA) then the event is assumed to occur at time Inf. cut can also be a dataframe, see details.

timescale

The timescale that cut refers to. Numeric or character.

new.state

The state to which a transition occur at time cut. It may be a single value, which is then applied to all rows of data, or a vector with a separate value for each row

new.scale

Name of the timescale defined as "time since entry to new.state". If TRUE a name for the new scale is contructed. See details.

split.states

Should states that are not precursor states be split according to whether the intermediate event has occurred.

progressive

a logical flag that determines the changes to exit status. See details.

precursor.states

an optional vector of states to be considered as "less severe" than new.state. See Details below

count

logical indicating wheter the countLexis options should be used. Specifying count=TRUE amounts to calling countLexis, and the arguments new.state, progressive and precursor

Value

• A Lexis object, for which each follow-up interval containing the cut point is split in two: one before and one after the cut point. An extra time-scale is added; the time since the event at cut. This is NA for any follow-up prior to the intermediate event.

Details

The cutLexis function allows a number of different ways of specifying the cutpoints and of modifying the status variable.

If the cut argument is a dataframe it must have columns lex.id, cut and new.state. The values of lex.id must be unique. In this case it is assumed that each row represents a cutpoint (on the timescale indicated in the argument timescale). This cutpoint will be applied to all records in data with the corresponding lex.id. This makes it possible to apply cutLexis to a split Lexis object.

If a new.state argument is supplied, the status variable is only modified at the time of the cut point. However, it is often useful to modify the status variable after the cutpoint when an important event occurs. There are three distinct ways of doing this.

If the progressive=TRUE argument is given, then a "progressive" model is assumed, in which the status can either remain the same or increase during follow-up, but never decrease. This assumes that the state variables lex.Cst and lex.Xst are either numeric or ordered factors. In this case, if new.state=X, then any exit status with a value less than X is replaced with X. The Lexis object must already be progressive, so that there are no rows for which the exit status is less than the entry status. If lex.Cst and lex.Xst are factors they must be ordered factors if progressive=TRUE is given.

As an alternative to the progressive argument, an explicit vector of precursor states, that are considered less severe than the new state, may be given. If new.state=X and precursor.states=c(Y,Z) then any exit status of Y or Z in the second interval is replaced with X and all other values for the exit status are retained.

The countLexis function is a variant of cutLexis when the cutpoint marks a recurrent event, and the status variable is used to count the number of events that have occurred. Times given in cut represent times of new events. Splitting with countLexis augments the status variable by 1. If the entry status is X and the exit status is Y before splitting, then after splitting the entry status is X, X+1 for the first and second intervals, respectively, and the exit status is X+1, Y+1 respectively.

See Also

splitLexis, Lexis, summary.Lexis

Examples

# A small artificial example
xx <- Lexis( entry=list(age=c(17,24,33,29),per=c(1920,1933,1930,1929)),
             duration=c(23,57,12,15), exit.status=c(1,2,1,2) )
xx
cut <- c(33,47,29,50)
cutLexis(xx, cut, new.state=3, precursor=1)
cutLexis(xx, cut, new.state=3, precursor=2)
cutLexis(xx, cut, new.state=3, precursor=1:2)
# The same as the last example
cutLexis(xx, cut, new.state=3)

# The same example with a factor status variable
yy <- Lexis(entry = list(age=c(17,24,33,29),per=c(1920,1933,1930,1929)),
            duration = c(23,57,12,15),
            entry.status = factor(rep("alpha",4),
            levels=c("alpha","beta","gamma")),
            exit.status = factor(c("alpha","beta","alpha","beta"),
            levels=c("alpha","beta","gamma")))

cutLexis(yy,c(33,47,29,50),precursor="alpha",new.state="gamma")
cutLexis(yy,c(33,47,29,50),precursor=c("alpha","beta"),new.state="aleph")

## Using a dataframe as cut argument
rl <- data.frame( lex.id=1:3, cut=c(19,53,26), timescale="age", new.state=3 )
rl
cutLexis( xx, rl )
cutLexis( xx, rl, precursor=1 )
cutLexis( xx, rl, precursor=0:2 )

## It is immaterial in what order splitting and cutting is done
xs <- splitLexis( xx, breaks=seq(0,100,10), time.scale="age" )
xs
xsC <- cutLexis(xs, rl, precursor=0 )

xC <- cutLexis( xx, rl, pre=0 )
xC
xCs <- splitLexis( xC, breaks=seq(0,100,10), time.scale="age" )
xCs