Repository Mirror for your Cloud Server and Webhosting

Type:

Package

Title:

Assurance Methods for Clinical Trials with a Delayed Treatment Effect

Version:

1.1.0

Description:

Provides functions for planning clinical trials subject to a delayed treatment effect using assurance-based methods. Includes two 'shiny' applications for interactive exploration, simulation, and visualisation of trial designs and outcomes. The methodology is described in: Salsbury JA, Oakley JE, Julious SA, Hampson LV (2024) "Assurance methods for designing a clinical trial with a delayed treatment effect" <doi:10.1002/sim.10136>, Salsbury JA, Oakley JE, Julious SA, Hampson LV (2024) "Adaptive clinical trial design with delayed treatment effects using elicited prior distributions" <doi:10.48550/arXiv.2509.07602>.

License:

MIT + file LICENSE

Encoding:

UTF-8

LazyData:

true

RoxygenNote:

7.3.3

Imports:

SHELF, shiny, stats, survival, nleqslv, nph, nphRCT, dplyr, rjags, rpact, magrittr, rlang, future.apply

Suggests:

testthat (≥ 3.0.0)

Config/testthat/edition:

Depends:

R (≥ 4.1.0)

Date:

2025-12-02

URL:

https://jamesalsbury.github.io/DTEAssurance/

NeedsCompilation:

Packaged:

2025-12-02 11:55:18 UTC; smp21js

Author:

James Salsbury

[aut, cre]

Maintainer:

James Salsbury <jsalsbury1@sheffield.ac.uk>

Repository:

CRAN

Date/Publication:

2025-12-02 12:20:02 UTC

Pipe operator

Description

See magrittr::%>% for details.

Usage

lhs %>% rhs

Arguments

lhs

A value or the magrittr placeholder.

rhs

A function call using the magrittr semantics.

Value

The result of calling rhs(lhs).

Calculate Bayesian Predictive Probability given interim data and posterior samples

Description

Calculate Bayesian Predictive Probability given interim data and posterior samples

Usage

BPP_func(
  data,
  posterior_df,
  control_distribution = "Exponential",
  n_c_planned,
  n_t_planned,
  rec_time_planned,
  df_cens_time,
  censoring_model,
  analysis_model,
  n_sims = 500
)

Arguments

data

A data frame containing interim survival data, censored at df_cens_time, with columns:

time Final observed/event time at the interim (on the analysis time scale).
group Treatment group indicator (e.g. "Control", "Treatment").
rec_time Recruitment (calendar) time.
pseudo_time time + rec_time (calendar time at event/censoring).
status Event indicator at the interim (1 = event, 0 = censored).
survival_time Observed follow-up time from randomisation to event/censoring at the interim.

posterior_df

A data frame of posterior samples with columns: lambda_c, delay_time and HR, corresponding to the control hazard, the delay (changepoint) time and the post-delay hazard ratio, respectively.

control_distribution

Distributional form assumed for the control arm: either "Exponential" (default) or "Weibull".

n_c_planned

Planned maximum number of patients in the control group.

n_t_planned

Planned maximum number of patients in the treatment group.

rec_time_planned

Planned maximum recruitment calendar time for the full trial.

df_cens_time

Calendar time at which df has been censored (interim analysis time).

censoring_model

A named list specifying the censoring mechanism for the future data:

method: one of "Time", "Events", or "IF".
time, events, IF: parameters for the corresponding method.

analysis_model

A named list specifying the final analysis and decision rule:

method: e.g. "LRT", "WLRT", or "MW".
alpha: one-sided type I error level.
alternative_hypothesis: direction of the alternative (e.g. "one.sided").
rho, gamma, t_star, s_star: additional parameters for WLRT or MW (if applicable).

n_sims

Number of predictive simulations to run (default is 1000).

Value

A single numeric value giving the Bayesian predictive probability of success at the final analysis under the specified design, censoring model and analysis model.

Examples

set.seed(123)
n <- 30
cens_time <- 15

time <- runif(n, 0, 12)
rec_time <- runif(n, 0, 12)


df <- data.frame(
  time = time,
  group = c(rep("Control", n/2), rep("Treatment", n/2)),
  rec_time = rec_time
)


df$pseudo_time <- df$time + df$rec_time
df$status <- df$pseudo_time < cens_time
df$survival_time <- ifelse(df$status == TRUE, df$time, cens_time - df$rec_time)


posterior_df <- data.frame(HR = rnorm(20, mean = 0.75, sd = 0.05),
                           delay_time = rep(0, 20),
                           lambda_c = rnorm(20, log(2)/9, sd = 0.01))


censoring_model = list(method = "Time", time = 25)
analysis_model = list(method = "LRT",
                      alpha = 0.025,
                      alternative_hypothesis = "one.sided")

BPP_outcome <- BPP_func(df,
           posterior_df,
           control_distribution = "Exponential",
           n_c_planned = n/2,
           n_t_planned = n/2,
           rec_time_planned = 12, df_cens_time = 15,
           censoring_model = censoring_model,
           analysis_model = analysis_model,
           n_sims = 10)

INTEREST data set

Description

A reconstructed survival data set for the INTEREST clinical trial

Usage

INTEREST

Format

A data frame with 710 rows and 2 variables:

Survival time: Survival Time (in months)
Status: Event indicator (0=Alive, 1=Dead)

Source

Reconstructed survival data set from the following publication: https://www.sciencedirect.com/science/article/pii/S0140673608617584?via%3Dihub

MCMC_sample

Description

An MCMC sample for the example given in Salsbury et al (2024)

Usage

MCMC_sample

Format

A data frame with 100000 rows and 1 variables:

x: Sample from the MAP prior

Source

A MCMC sample for the control group for the example given in https://onlinelibrary.wiley.com/doi/full/10.1002/sim.10136. Three historical data seta are used to generate a Meta-Analytic-Predictive Prior distribution

REVEL data set

Description

A reconstructed survival data set for the REVEL clinical trial

Usage

REVEL

Format

A data frame with 625 rows and 2 variables:

Survival time: Survival Time (in months)
Status: Event indicator (0=Alive, 1=Dead)

Source

Reconstructed survival data set from the following publication: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(14)60845-X/fulltext

ZODIAC data set

Description

A reconstructed survival data set for the ZODIAC clinical trial

Usage

ZODIAC

Format

A data frame with 697 rows and 2 variables:

Survival time: Survival Time (in months)
Status: Event indicator (0=Alive, 1=Dead)

Source

Reconstructed survival data set from the following publication: https://www.sciencedirect.com/science/article/abs/pii/S1470204510701327?via%3Dihub

Add recruitment time to a survival dataset

Description

Simulates recruitment timing for each patient in a survival dataset using either a power model or a piecewise constant (PWC) model. The function appends recruitment times and pseudo survival times (time from recruitment to event or censoring).

Usage

add_recruitment_time(
  data,
  rec_method,
  rec_period = NULL,
  rec_power = NULL,
  rec_rate = NULL,
  rec_duration = NULL
)

Arguments

data

A dataframe containing survival data with columns: time, status, and group

rec_method

Recruitment method: "power" for power model or "PWC" for piecewise constant model

rec_period

Period length for the power model

rec_power

Power parameter for the power model

rec_rate

Comma-separated string of recruitment rates for the PWC model

rec_duration

Comma-separated string of durations corresponding to each rate in the PWC model

Value

A dataframe with two additional columns:

rec_time: Simulated recruitment time for each patient
pseudo_time: Time from recruitment to event or censoring

Class: data.frame

Examples

set.seed(123)
df <- data.frame(
  time = rexp(20, rate = 0.1),
  status = rbinom(20, 1, 0.8),
  group = rep(c("Control", "Treatment"), each = 10)
)
recruited <- add_recruitment_time(df, rec_method = "power", rec_period = 12, rec_power = 1)
head(recruited)

Launch the 'shiny' adaptive assurance app

Description

Launches a 'shiny' application to simulate group sequential trials with delayed treatment effects (DTE) using elicited prior distributions. The app allows interactive exploration of trial designs and assurance calculations.

Usage

assurance_adaptive_shiny_app()

Value

No return value, called for side effects (invisibly returns NULL). The function launches an interactive 'shiny' application.

Examples


# Launch the interactive Shiny app
assurance_adaptive_shiny_app()

Launch the 'shiny' Assurance app

Description

Launches a 'shiny' application to calculate assurance for clinical trials where delayed treatment effects (DTE) may be present. The app allows elicitation of prior distributions and calculates assurance metrics.

Usage

assurance_shiny_app()

Value

No return value, called for side effects (invisibly returns NULL). The function launches an interactive 'shiny' application.

Examples


# Launch the interactive Shiny app
assurance_shiny_app()

Calculate Assurance for a Trial with a Delayed Treatment Effect

Description

Simulates operating characteristics for a clinical trial under prior uncertainty about a delayed treatment effect. The function integrates beliefs about control survival, treatment delay, post-delay hazard ratio, recruitment, censoring, and analysis method to estimate assurance and other trial metrics.

Usage

calc_dte_assurance(
  n_c,
  n_t,
  control_model,
  effect_model,
  censoring_model,
  recruitment_model,
  analysis_model,
  n_sims = 1000
)

Arguments

n_c

Vector of control group sample sizes

n_t

Vector of treatment group sample sizes

control_model

A named list specifying the control arm survival distribution:

dist: Distribution type ("Exponential" or "Weibull")
parameter_mode: Either "Fixed" or "Distribution"
fixed_type: If "Fixed", specify as "Parameters" or "Landmark"
lambda, gamma: Scale and shape parameters
t1, t2: Landmark times
surv_t1, surv_t2: Survival probabilities at landmarks
t1_Beta_a, t1_Beta_b, diff_Beta_a, diff_Beta_b: Beta prior parameters

effect_model

A named list specifying beliefs about the treatment effect:

delay_SHELF, HR_SHELF: SHELF objects encoding beliefs
delay_dist, HR_dist: Distribution types ("hist" by default)
P_S: Probability that survival curves separate
P_DTE: Probability of delayed separation, conditional on separation

censoring_model

A named list specifying the censoring mechanism:

method: "Time", "Events", or "IF"
time, events, IF: Parameters for each method

recruitment_model

A named list specifying the recruitment process:

method: "power" or "PWC"
period, power: Parameters for power model
rate, duration: Comma-separated strings for PWC model

analysis_model

A named list specifying the statistical test and decision rule:

method: "LRT", "WLRT", or "MW"
alpha, alternative_hypothesis: Type I error and hypothesis direction
rho, gamma, t_star, s_star: Parameters for WLRT or MW
success_threshold_HR: Optional threshold for declaring success

n_sims

Number of simulations to run (default = 1000)

Value

A named list containing:

assurance: Estimated assurance (probability of success under prior uncertainty)
CI: 95% confidence interval for assurance
duration: Mean trial duration across simulations
sample_size: Mean sample size across simulations
diagnostics: Additional diagnostics if success_threshold_HR is specified

Class: list

Examples

set.seed(123)
control_model <- list(dist = "Exponential", parameter_mode = "Fixed",
fixed_type = "Parameters", lambda = 0.1)
effect_model <- list(delay_SHELF = SHELF::fitdist(c(3, 4, 5),
probs = c(0.25, 0.5, 0.75), lower = 0, upper = 10),
delay_dist = "gamma",
HR_SHELF = SHELF::fitdist(c(0.55, 0.6, 0.7), probs = c(0.25, 0.5, 0.75), lower = 0, upper = 1.5),
HR_dist = "gamma",
P_S = 1, P_DTE = 0)
censoring_model <- list(method = "Time", time = 12)
recruitment_model <- list(method = "power", period = 12, power = 1)
analysis_model <- list(method = "LRT", alpha = 0.025, alternative_hypothesis = "two.sided")
result <- calc_dte_assurance(n_c = 300, n_t = 300,
                                     control_model = control_model,
                                     effect_model = effect_model,
                                     censoring_model = censoring_model,
                                     recruitment_model = recruitment_model,
                                     analysis_model = analysis_model,
                                     n_sims = 10)
str(result)

Calculates operating characteristics for a Group Sequential Trial with a Delayed Treatment Effect

Description

Simulates assurance and operating characteristics for a group sequential trial under prior uncertainty about a delayed treatment effect. The function integrates beliefs about control survival, treatment delay, post-delay hazard ratio, recruitment, and group sequential design (GSD) parameters.

Usage

calc_dte_assurance_adaptive(
  n_c,
  n_t,
  control_model,
  effect_model,
  recruitment_model,
  GSD_model,
  analysis_model = NULL,
  n_sims = 1000
)

Arguments

n_c

Control group sample size

n_t

Treatment group sample size

control_model

A named list specifying the control arm survival distribution:

dist: Distribution type ("Exponential" or "Weibull")
parameter_mode: Either "Fixed" or "Distribution"
fixed_type: If "Fixed", specify as "Parameters" or "Landmark"
lambda, gamma: Scale and shape parameters
t1, t2: Landmark times
surv_t1, surv_t2: Survival probabilities at landmarks
t1_Beta_a, t1_Beta_b, diff_Beta_a, diff_Beta_b: Beta prior parameters

effect_model

A named list specifying beliefs about the treatment effect:

delay_SHELF, HR_SHELF: SHELF objects encoding beliefs
delay_dist, HR_dist: Distribution types ("hist" by default)
P_S: Probability that survival curves separate
P_DTE: Probability of delayed separation, conditional on separation

recruitment_model

A named list specifying the recruitment process:

method: "power" or "PWC"
period, power: Parameters for power model
rate, duration: Comma-separated strings for PWC model

GSD_model

A named list specifying the group sequential design:

events: Total number of events
alpha_spending: Cumulative alpha spending vector
alpha_IF: Information Fraction at which we look for efficacy
futility_type: beta (for beta-spending), BPP (for Bayesian Predictive Probability) or none
futility_IF: Information Fraction at which we look for futility
beta_spending: Cumulative beta spending vector
BPP_threshold: BPP value at which we will stop for futility

analysis_model

A named list specifying the final analysis and decision rule:

method: e.g. "LRT", "WLRT", or "MW".
alpha: one-sided type I error level.
alternative_hypothesis: direction of the alternative (e.g. "one.sided").
rho, gamma, t_star, s_star: additional parameters for WLRT or MW (if applicable).

n_sims

Number of simulations to run (default = 1000)

Value

A data frame with one row per simulated trial and the following columns:

Trial: Simulation index
IF: Information fraction label used at the decision point
Decision: Interim decision outcome (e.g., "Continue", "Stop for efficacy", "Stop for futility")
StopTime: Time at which the trial stopped or completed
SampleSize: Total sample size at the time of decision
Final_Decision: Final classification of trial success based on the test statistic and threshold

Class: data.frame

Examples

set.seed(123)
control_model <- list(dist = "Exponential", parameter_mode = "Fixed",
fixed_type = "Parameters", lambda = 0.1)
effect_model <- list(P_S = 1, P_DTE = 0,
HR_SHELF = SHELF::fitdist(c(0.6, 0.65, 0.7), probs = c(0.25, 0.5, 0.75), lower = 0, upper = 2),
HR_dist = "gamma",
delay_SHELF = SHELF::fitdist(c(3, 4, 5), probs = c(0.25, 0.5, 0.75), lower = 0, upper = 10),
delay_dist = "gamma"
)
recruitment_model <- list(method = "power", period = 12, power = 1)
GSD_model <- list(events = 300, alpha_spending = c(0.0125, 0.025),
                  alpha_IF = c(0.75, 1), futility_type = "none")
result <- calc_dte_assurance_adaptive(n_c = 300, n_t = 300,
                        control_model = control_model,
                        effect_model = effect_model,
                        recruitment_model = recruitment_model,
                        GSD_model = GSD_model,
                        n_sims = 10)
str(result)

Function to calculate the 'optimal' BPP threshold value

Description

Function to calculate the 'optimal' BPP threshold value

Usage

calibrate_BPP_threshold(
  n_c,
  n_t,
  control_model,
  effect_model,
  recruitment_model,
  IA_model,
  analysis_model,
  data_generating_model,
  n_sims = 100
)

Arguments

n_c

Number of control patients

n_t

Number of treatment patients

control_model

A named list specifying the control arm survival distribution:

dist: Distribution type ("Exponential" or "Weibull")
parameter_mode: Either "Fixed" or "Distribution"
fixed_type: If "Fixed", specify as "Parameters" or "Landmark"
lambda, gamma: Scale and shape parameters
t1, t2: Landmark times
surv_t1, surv_t2: Survival probabilities at landmarks
t1_Beta_a, t1_Beta_b, diff_Beta_a, diff_Beta_b: Beta prior parameters

effect_model

A named list specifying beliefs about the treatment effect:

delay_SHELF, HR_SHELF: SHELF objects encoding beliefs
delay_dist, HR_dist: Distribution types ("hist" by default)
P_S: Probability that survival curves separate
P_DTE: Probability of delayed separation, conditional on separation

recruitment_model

A named list specifying the recruitment process:

method: "power" or "PWC"
period, power: Parameters for power model
rate, duration: Comma-separated strings for PWC model

IA_model

A named list specifying the censoring mechanism for the future data:

events: Number of events which is 100% information fraction
IF: The information fraction at which to censor and calculate BPP

analysis_model

A named list specifying the final analysis and decision rule:

method: e.g. "LRT", "WLRT", or "MW".
alpha: one-sided type I error level.
alternative_hypothesis: direction of the alternative (e.g. "one.sided").
rho, gamma, t_star, s_star: additional parameters for WLRT or MW (if applicable).

data_generating_model

A named list specifying the parameters for the data-generating mechanism

lambda_c: hazard rate for the control group
delay_time: time at which the treatment starts to take effect
post_delay_HR: hazard ratio, after delay_time

n_sims

Number of data sets to simulate (default is 100).

Value

A vector of length n_sims corresponding to the value of BPP for each simulated trial

Examples

set.seed(123)
control_model = list(dist = "Exponential",
                     parameter_mode = "Distribution",
                     t1 = 12,
                     t1_Beta_a = 20,
                     t1_Beta_b = 32)

effect_model = list(delay_SHELF = SHELF::fitdist(c(5.5, 6, 6.5),
                    probs = c(0.25, 0.5, 0.75), lower = 0, upper = 12),
                    delay_dist = "gamma",
                    HR_SHELF = SHELF::fitdist(c(0.5, 0.6, 0.7),
                    probs = c(0.25, 0.5, 0.75), lower = 0, upper = 1),
                    HR_dist = "gamma",
                    P_S = 1,
                    P_DTE = 0)

recruitment_model <- list(method = "power", period = 12, power = 1)

IA_model = list(events = 20, IF = 0.5)

analysis_model = list(method = "LRT",
                      alpha = 0.025,
                      alternative_hypothesis = "one.sided")


data_generating_model = list(lambda_c = log(2)/12,
                             delay_time = 3,
                             post_delay_HR = 0.75)


threshold <- calibrate_BPP_threshold(n_c = 15, n_t = 15,
                     control_model = control_model,
                     effect_model = effect_model,
                     recruitment_model = recruitment_model,
                     IA_model = IA_model,
                     analysis_model = analysis_model,
                     data_generating_model = data_generating_model,
                     n_sims = 2)

Function to calculate the 'optimal' information fraction to calculate BPP

Description

Function to calculate the 'optimal' information fraction to calculate BPP

Usage

calibrate_BPP_timing(
  n_c,
  n_t,
  control_model,
  effect_model,
  recruitment_model,
  IA_model,
  analysis_model,
  n_sims = 50
)

Arguments

n_c

Number of control patients

n_t

Number of treatment patients

control_model

A named list specifying the control arm survival distribution:

dist: Distribution type ("Exponential" or "Weibull")
parameter_mode: Either "Fixed" or "Distribution"
fixed_type: If "Fixed", specify as "Parameters" or "Landmark"
lambda, gamma: Scale and shape parameters
t1, t2: Landmark times
surv_t1, surv_t2: Survival probabilities at landmarks
t1_Beta_a, t1_Beta_b, diff_Beta_a, diff_Beta_b: Beta prior parameters

effect_model

A named list specifying beliefs about the treatment effect:

delay_SHELF, HR_SHELF: SHELF objects encoding beliefs
delay_dist, HR_dist: Distribution types ("hist" by default)
P_S: Probability that survival curves separate
P_DTE: Probability of delayed separation, conditional on separation

recruitment_model

A named list specifying the recruitment process:

method: "power" or "PWC"
period, power: Parameters for power model
rate, duration: Comma-separated strings for PWC model

IA_model

A named list specifying the censoring mechanism for the future data:

events: Number of events which is 100% information fraction
IF: The information fraction at which to censor and calculate BPP

analysis_model

A named list specifying the final analysis and decision rule:

method: e.g. "LRT", "WLRT", or "MW".
alpha: one-sided type I error level.
alternative_hypothesis: direction of the alternative (e.g. "one.sided").
rho, gamma, t_star, s_star: additional parameters for WLRT or MW (if applicable).

n_sims

Number of data sets to simulate (default is 100).

Value

A vector of length n_sims corresponding to the value of BPP for each simulated trial

Examples



#' set.seed(123)
control_model = list(dist = "Exponential",
                     parameter_mode = "Distribution",
                     t1 = 12,
                     t1_Beta_a = 20,
                     t1_Beta_b = 32)

effect_model = list(delay_SHELF = SHELF::fitdist(c(5.5, 6, 6.5),
                    probs = c(0.25, 0.5, 0.75), lower = 0, upper = 12),
                    delay_dist = "gamma",
                    HR_SHELF = SHELF::fitdist(c(0.5, 0.6, 0.7),
                    probs = c(0.25, 0.5, 0.75), lower = 0, upper = 1),
                    HR_dist = "gamma",
                    P_S = 1,
                    P_DTE = 0)

recruitment_model <- list(method = "power", period = 12, power = 1)

IA_model = list(events = 20, IF = 0.5)

analysis_model = list(method = "LRT",
                      alpha = 0.025,
                      alternative_hypothesis = "one.sided")

timing <- calibrate_BPP_timing(n_c = 15, n_t = 15,
                     control_model = control_model,
                     effect_model = effect_model,
                     recruitment_model = recruitment_model,
                     IA_model = IA_model,
                     analysis_model = analysis_model,
                     n_sims = 2)

Censor a survival dataset

Description

Applies administrative censoring to a survival dataset using one of three methods: fixed time, fixed number of events, or fixed information fraction. The input data must contain columns for pseudo survival time, recruitment time, and observed time.

Usage

cens_data(
  data,
  cens_method = "Time",
  cens_time = NULL,
  cens_IF = NULL,
  cens_events = NULL
)

Arguments

data

A dataframe containing uncensored survival data with columns: pseudo_time, rec_time, and time

cens_method

Censoring method: "Time" (default), "Events", or "IF"

cens_time

Time point for censoring (required if cens_method = "Time")

cens_IF

Information fraction for censoring (required if cens_method = "IF")

cens_events

Number of events for censoring (required if cens_method = "Events")

Value

A list containing:

data: Censored dataframe with updated status and filtered rows
cens_events: Number of events used for censoring (if applicable)
cens_time: Time point used for censoring
sample_size: Number of patients remaining after censoring

Examples

set.seed(123)
df <- data.frame(
  pseudo_time = rexp(20, rate = 0.1),
  rec_time = runif(20, 0, 12),
  time = rexp(20, rate = 0.1)
)
censored <- cens_data(df, cens_method = "Time", cens_time = 10)
str(censored)

Simulates survival times for a delayed treatment effect (DTE) scenario, where the treatment group experiences a delayed onset of benefit. Control and treatment groups are generated under exponential or Weibull distributions.

Description

Simulates survival times for a delayed treatment effect (DTE) scenario, where the treatment group experiences a delayed onset of benefit. Control and treatment groups are generated under exponential or Weibull distributions.

Usage

sim_dte(
  n_c,
  n_t,
  lambda_c,
  delay_time,
  post_delay_HR,
  dist = "Exponential",
  gamma_c = NULL
)

Arguments

n_c

The number of patients in the control group

n_t

The number of patients in the treatment group

lambda_c

The baseline hazard rate for the control group

delay_time

The length of delay before treatment effect begins

post_delay_HR

The hazard ratio after the delay period

dist

The distribution for the control group; must be one of "Exponential" (default) or "Weibull"

gamma_c

The shape parameter for the Weibull distribution (only used if dist = "Weibull")

Value

A data frame with two columns:

time

Simulated survival times

group

Group assignment: "Control" or "Treatment"

Class: data.frame

Examples

set.seed(123)
sim_data <- sim_dte(n_c = 10, n_t = 10, lambda_c = 0.1,
                    delay_time = 6, post_delay_HR = 0.6)
head(sim_data)

Calculate statistical significance on a survival dataset

Description

Performs a survival analysis using either the standard log-rank test (LRT) or a weighted log-rank test (WLRT). The function estimates the hazard ratio and determines whether the result is statistically significant based on the specified alpha level and alternative hypothesis.

Usage

survival_test(
  data,
  analysis_method = "LRT",
  alternative = "one.sided",
  alpha = 0.05,
  rho = 0,
  gamma = 0,
  t_star = NULL,
  s_star = NULL
)

Arguments

data

A dataframe containing survival data. Must include columns for survival time, event status, and treatment group.

analysis_method

Method of analysis: "LRT" (default) for standard log-rank test, or "WLRT" for weighted log-rank test.

alternative

String specifying the alternative hypothesis. Must be one of "one.sided" or "two.sided" (default).

alpha

Type I error threshold for significance testing.

rho

Rho parameter for the Fleming-Harrington weighted log-rank test.

gamma

Gamma parameter for the Fleming-Harrington weighted log-rank test.

t_star

Parameter t^* used in modestly weighted tests.

s_star

Parameter s^* used in modestly weighted tests.

Value

A list containing:

Signif: Logical indicator of statistical significance based on the chosen test and alpha level.
observed_HR: Estimated hazard ratio from a Cox proportional hazards model.

Examples

set.seed(123)
df <- data.frame(
  survival_time = rexp(40, rate = 0.1),
  status = rbinom(40, 1, 0.8),
  group = rep(c("Control", "Treatment"), each = 20)
)
result <- survival_test(df, analysis_method = "LRT", alpha = 0.05)
str(result)

Update prior distributions using interim survival data

Description

This function updates elicited priors (defined through SHELF objects and parametric prior distributions) using interim survival data under a delayed-effect, piecewise-exponential model for the treatment arm and an exponential or Weibull model for the control arm.

Usage

update_priors(data, control_model, effect_model, n_samples = 1000)

Arguments

data

A data frame containing interim survival data with columns:

survival_time Observed time from randomisation to event/censoring.
status Event indicator (1 = event, 0 = censored).
group Group identifier (e.g., "Control", "Treatment").

control_model

A named list specifying the control arm survival distribution:

dist: Distribution type ("Exponential" or "Weibull")
parameter_mode: Either "Fixed" or "Distribution"
fixed_type: If "Fixed", specify as "Parameters" or "Landmark"
lambda, gamma: Scale and shape parameters
t1, t2: Landmark times
surv_t1, surv_t2: Survival probabilities at landmarks
t1_Beta_a, t1_Beta_b, diff_Beta_a, diff_Beta_b: Beta prior parameters

effect_model

A named list specifying beliefs about the treatment effect:

delay_SHELF, HR_SHELF: SHELF objects encoding beliefs
delay_dist, HR_dist: Distribution types ("hist" by default)
P_S: Probability that survival curves separate
P_DTE: Probability of delayed separation, conditional on separation

n_samples

Number of posterior samples to generate (default: 1000).

Value

A data frame containing Monte Carlo samples from the updated (posterior) distribution of the model parameters. Columns normally include:

lambda_c Posterior samples for the control hazard parameter.
delay_time Posterior samples for the delay/changepoint time T.
HR Posterior samples for the post-delay hazard ratio.
gamma_c (only if control_distribution = "Weibull") Posterior samples for the Weibull shape parameter.

Priors for lambda_c, T, and HR are constructed from elicited distributions using the SHELF framework, then updated through sampling-based posterior inference.

Examples

set.seed(123)
interim_data = data.frame(survival_time = runif(10, min = 0, max = 10),
status = rbinom(10, size = 1, prob = 0.5),
group = c(rep("Control", 5), rep("Treatment", 5)))
control_model = list(dist = "Exponential",
                     parameter_mode = "Distribution",
                     t1 = 12,
                     t1_Beta_a = 20,
                     t1_Beta_b = 32)

effect_model = list(delay_SHELF = SHELF::fitdist(c(5.5, 6, 6.5),
                    probs = c(0.25, 0.5, 0.75), lower = 0, upper = 12),
                    delay_dist = "gamma",
                    HR_SHELF = SHELF::fitdist(c(0.5, 0.6, 0.7),
                    probs = c(0.25, 0.5, 0.75), lower = 0, upper = 1),
                    HR_dist = "gamma",
                    P_S = 1,
                    P_DTE = 0)

posterior_df <- update_priors(
  data = interim_data,
  control_model = control_model,
  effect_model = effect_model,
  n_samples = 10)

Package imports

Description

Package imports