| Lexis {Epi} | R Documentation |
Create an object of class Lexis to represent follow-up on
multiple time scales.
Lexis(entry, exit, duration, entry.status = 0, exit.status = 0, id, data,
merge=TRUE)
entry |
a named list of entry times. Each element of the list is a numeric variable representing the entry time on the named time scale. All time scales must have the same units (e.g. years) |
exit |
a named list of exit times |
duration |
a numeric vector giving the duration of follow-up |
entry.status |
a vector giving the status at entry |
exit.status |
a vector giving status at exit. Any change in status during follow-up is assumed to take place exactly at the exit time |
id |
a vector giving a unique identity value for each row of the Lexis object |
data |
an optional data frame, list, or environment containing
the variables. If not found in data, the variables are
taken from the environment from which Lexis was called |
merge |
a logical flag. If TRUE then the data
argument will be coerced to a data frame and then merged with
the resulting Lexis object |
The analysis of long-term population-based follow-up studies typically
requires multiple time scales to be taken into account, such as
age, calender time, or time since an event. A Lexis object is
a data frame with additional attributes that allows these multiple time
dimensions of follow-up to be managed.
Lexis objects are named after the German gemographer Wilhelm Lexis (1837-1914), who is credited with the invention of the "Lexis diagram" for representing population dynamics simultaneously by age, period and cohort.
The Lexis function creates a minimal Lexis object with
only those variables required to define the follow-up history in each
row. Additional variables can be merged into the Lexis object
using the merge method for Lexis objects.
An object of class Lexis. This is represented as a data frame
with a column for each time scale, and additional columns with the
following names:
lex.id |
Identification of the inidvidual |
lex.deltat |
Duration of follow-up |
lex.status1 |
Entry status |
lex.status2 |
Exit status |
If merge=TRUE then the Lexis object will also contain
all variables from the data argument.
Only two of the three arguments entry, exit and
duration need to be given. If the third parameter is missing,
it is imputed. If duration is imputed, it must be the same on
all time scales.
Martyn Plummer
plot.Lexis, splitLexis,
merge.Lexis, entry,
timeScales,
timeBand