tvc {simPH} | R Documentation |
Create a time interaction variable
Description
tvc
creates a time interaction variable that can be used in a coxph
model (or any other model with time interactions)
Usage
tvc(data, b, tvar, tfun = "linear", pow = NULL, vector = FALSE)
Arguments
data |
a data frame |
b |
the non-time interacted variable's name. Either a single value or a vector of variable names can be entered. |
tvar |
the time variable's name |
tfun |
function of time that btvc was multiplied by. Default is
|
pow |
if |
vector |
logical. Whether or not to return one vector a or a data frame.
Can only be used if only one |
Details
Interacts a variable with a specified function of time. Possible
functions of time include 'linear'
, natural 'log'
, and
exponentiated ('power'
).
Value
a data frame or vector. If a data frame is returned it will include
all of the original variables as well as the interactions denoted by a
variable name 'bn
_tfun
', where bn
is one variable name
from b
and tfun
as entered into the function.
See Also
SurvExpand
, simGG.simtvc
,
coxsimtvc
, survival
, and coxph
Examples
# Load Golub & Steunenberg (2007) Data
data('GolubEUPData')
# Subset PURELY TO SPEED UP THE EXAMPLE
GolubEUPData <- GolubEUPData[1:500, ]
# Expand data into equally spaced time intervals
GolubEUPData <- SurvExpand(GolubEUPData, GroupVar = 'caseno',
Time = 'begin', Time2 = 'end', event = 'event')
# Create natural log time interaction with the qmv variable
GolubEUPData$Lqmv <- tvc(GolubEUPData, b = 'qmv', tvar = 'end', tfun = 'log',
vector = TRUE)
# Create interactions for a vector of variables
BaseVars <- c('qmv', 'backlog', 'coop', 'codec', 'qmvpostsea', 'thatcher')
Test <- tvc(GolubEUPData, b = BaseVars, tvar = 'end', tfun = 'log')