simulate_cross_sectional_tvem_example {tvem}

simulate_cross_sectional_tvem_example: Simulate a cross-sectional dataset for demonstrating tvem.

Description

This differs from what simulate_tvem_example does, in that each participant (subject) is only measured at a single measurement time, but the measurement time of each subject is random. This might simulate a sample of people of many different ages, where age is treated as a continuous number.

Usage

simulate_cross_sectional_tvem_example(
  n_subjects = 300,
  min_time = 7,
  max_time = 7,
  simulate_binary = FALSE,
  sigma_x1 = 2,
  sigma_x2 = 2,
  truncate_for_realism = TRUE,
  round_digits = 3,
  sigma_y = 1.5,
  mu_x1_function = function(t) {
     6 - 2 * sqrt(pmax(0, ((t - min(t))/7) - 0.2))
 },
  mu_x2_function = function(t) {
     3 + sqrt(pmax(0, ((t - min(t))/7) - 0.5))
 },
  beta0_y_function = function(t) {
     1 - 0.3 * sqrt((t - min(t))/7)
 },
  beta1_y_function = function(t) {
     0.5 * ((t - min(t))/7)^2
 },
  beta2_y_function = function(t) {
     rep(0.2, length(t))
 }
)

Arguments

n_subjects

Number of subjects in dataset

min_time

The time point at the end of the simulated time interval

max_time

The time point at the end of the simulated time interval

simulate_binary

Whether the simulated data should be binary

sigma_x1

Standard deviation of covariate 1, assumed homoskedastic over time

sigma_x2

Standard deviation of covariate 2, assumed homoskedastic over time

truncate_for_realism

Whether to prevent simulated values from going below 0 or above 10, in order to imitate survey data; used only for normally distributed outcomes. Set this to FALSE if you are running a simulation, in order to avoid losing coverage due to departing from the parametric model.

round_digits

Number of digits at which to round the generated data; used only for normally distributed outcomes

sigma_y

Error standard deviation of y, only used if the outcomes are to be normal rather than binary

mu_x1_function

Mean of covariate 1 as function of time

mu_x2_function

Mean of covariate 2 as function of time

beta0_y_function

TVEM intercept as function of time

beta1_y_function

TVEM coefficient of covariate 1 as function of time

beta2_y_function

TVEM coefficient of covariate 2 as function of time

Details

By default, the data-generating model has a time-varying intercept, and two time-varying covariates named x1 and x2. x1 has a time-varying effect and x2 has a time-invariant effect.

Value

A simulated dataset with the following variables:

subject_id

Subject ID

time

Observation time

x1

First covariate

x2

Second covariate

y

Outcome variable

Examples

set.seed(16802)
the_data <- simulate_tvem_example(simulate_binary=TRUE)