addPeriods {simstudy}

Create longitudinal/panel data

Description

Create longitudinal/panel data

Usage

addPeriods(
  dtName,
  nPeriods = NULL,
  idvars = "id",
  timevars = NULL,
  timevarName = "timevar",
  timeid = "timeID",
  perName = "period",
  periodVec = NULL
)

Arguments

dtName

Name of existing data table

nPeriods

Number of time periods for each record

idvars

Names of index variables (in a string vector) that will be repeated during each time period

timevars

Names of time dependent variables. Defaults to NULL.

timevarName

Name of new time dependent variable

timeid

Variable name for new index field. Defaults to "timevar"

perName

Variable name for period field. Defaults to "period"

periodVec

Vector of period times. Defaults to NULL

Details

It is possible to generate longitudinal data with varying numbers of measurement periods as well as varying time intervals between each measurement period. This is done by defining specific variables in the data set that define the number of observations per subject and the average interval time between each observation. nCount defines the number of measurements for an individual; mInterval specifies the average time between intervals for a subject; and vInterval specifies the variance of those interval times. If mInterval is not defined, no intervals are used. If vInterval is set to 0 or is not defined, the interval for a subject is determined entirely by the mean interval. If vInterval is greater than 0, time intervals are generated using a gamma distribution with specified mean and dispersion. If either nPeriods or timevars is specified, that will override any nCount, mInterval, and vInterval data.

periodVec is used to specify measurement periods that are different the default counting variables. If periodVec is not specified, the periods default to 0, 1, ... n-1, with n periods. If periodVec is specified as c(x_1, x_2, ... x_n), then x_1, x_2, ... x_n represent the measurement periods.

Value

An updated data.table that that has multiple rows per observation in dtName

Examples

tdef <- defData(varname = "T", dist = "binary", formula = 0.5)
tdef <- defData(tdef, varname = "Y0", dist = "normal", formula = 10, variance = 1)
tdef <- defData(tdef, varname = "Y1", dist = "normal", formula = "Y0 + 5 + 5 * T", variance = 1)
tdef <- defData(tdef, varname = "Y2", dist = "normal", formula = "Y0 + 10 + 5 * T", variance = 1)

dtTrial <- genData(5, tdef)
dtTrial

dtTime <- addPeriods(dtTrial,
  nPeriods = 3, idvars = "id",
  timevars = c("Y0", "Y1", "Y2"), timevarName = "Y"
)
dtTime

# Varying # of periods and intervals - need to have variables
# called nCount and mInterval

def <- defData(varname = "xbase", dist = "normal", formula = 20, variance = 3)
def <- defData(def, varname = "nCount", dist = "noZeroPoisson", formula = 6)
def <- defData(def, varname = "mInterval", dist = "gamma", formula = 30, variance = .01)
def <- defData(def, varname = "vInterval", dist = "nonrandom", formula = .07)

dt <- genData(200, def)
dt[id %in% c(8, 121)]

dtPeriod <- addPeriods(dt)
dtPeriod[id %in% c(8, 121)] # View individuals 8 and 121 only