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Analyze Power for a Linear RMST Model via Simulation

Source: R/linear_ipcw_boot.R
linear.power.boot.Rd

Performs a power analysis for given sample sizes based on the direct linear regression model for RMST, using a bootstrap simulation approach.

Usage

linear.power.boot(
  pilot_data,
  time_var,
  status_var,
  arm_var,
  sample_sizes,
  linear_terms = NULL,
  L,
  n_sim = 1000,
  alpha = 0.05
)

Arguments

pilot_data

A data.frame with pilot study data.

time_var

A character string for the time-to-event variable.

status_var

A character string for the event status variable.

arm_var

A character string for the treatment arm variable.

sample_sizes

A numeric vector of sample sizes per arm to calculate power for.

linear_terms

Optional character vector of other covariates for the linear model.

L

The numeric truncation time for RMST.

n_sim

The number of bootstrap simulations to run for each sample size.

alpha

The significance level (Type I error rate).

Value

A list containing:

results_data

A data.frame of sample sizes and corresponding estimated power.

results_plot

A ggplot object visualizing the power curve.

results_summary

A data.frame with summary statistics for the estimated treatment effect from the largest sample size simulation.

Details

This function estimates power by generating a number of bootstrap samples (n_sim) from the provided pilot data by resampling with replacement. For each bootstrap sample, it performs the following steps:

  1. Estimates the censoring distribution using the Kaplan-Meier method (survival::survfit).

  2. Calculates Inverse Probability of Censoring Weights (IPCW) for each observation.

  3. Fits a weighted linear model (stats::lm) to the RMST of the uncensored subjects.

  4. Extracts the p-value for the treatment arm_var coefficient.

The final power for a given sample size is the proportion of the n_sim simulations where this p-value is less than the significance level alpha. This simulation-based approach is robust but can be computationally intensive.

Note

status_var should be 1 for an event, 0 for censored. arm_var should be 1 for treatment, 0 for control.

Examples

if (FALSE) { # \dontrun{
pilot_df <- data.frame(
  time = rexp(100, 0.1),
  status = rbinom(100, 1, 0.7),
  arm = rep(0:1, each = 50),
  age = rnorm(100, 60, 8)
)
# Introduce a treatment effect for a more interesting example
pilot_df$time[pilot_df$arm == 1] <- pilot_df$time[pilot_df$arm == 1] * 1.5

power_results <- linear.power.boot(
  pilot_data = pilot_df,
  time_var = "time",
  status_var = "status",
  arm_var = "arm",
  linear_terms = "age",
  sample_sizes = c(100, 150, 200),
  L = 10,
  n_sim = 200 # Use more simulations in practice (e.g., 1000)
)
print(power_results$results_data)
print(power_results$results_plot)
} # }