hesim (version 0.5.5)

CohortDtstmTrans: Transitions for a cohort discrete time state transition model

Description

Simulate health state transitions in a cohort discrete time state transition model.

Format

An R6::R6Class object.

Public fields

params

Parameters for simulating health state transitions. Supports objects of class tparams_transprobs or params_mlogit_list.

input_data

An object of class input_mats.

cycle_length

The length of a model cycle in terms of years. The default is 1 meaning that model cycles are 1 year long.

absorbing

A numeric vector denoting the states that are absorbing states; i.e., states that cannot be transitioned from. Each element should correspond to a state_id, which should, in turn, be the index of the health state.

Active bindings

start_stateprobs

A non-negative vector with length equal to the number of health states containing the probability that the cohort is in each health state at the start of the simulation. For example, if there were three states and the cohort began the simulation in state 1, then start_stateprobs = c(1, 0, 0). Automatically normalized to sum to 1. If NULL, then a vector with the first element equal to 1 and all remaining elements equal to 0.

trans_mat

A transition matrix describing the states and transitions in a discrete-time multi-state model. Only required if the model is parameterized using multinomial logistic regression. The (i,j) element represents a transition from state i to state j. Each possible transition from row i should be based on a separate multinomial logistic regression and ordered from 0 to K - 1 where K is the number of possible transitions. Transitions that are not possible should be NA. and the reference category for each row should be 0.

Methods

Public methods

• CohortDtstmTrans$new()

• CohortDtstmTrans$sim_stateprobs()

• CohortDtstmTrans$clone()

---

Method new()

Create a new CohortDtstmTrans object.

Usage

CohortDtstmTrans$new(
  params,
  input_data = NULL,
  trans_mat = NULL,
  start_stateprobs = NULL,
  cycle_length = 1,
  absorbing = NULL
)

Arguments

params

The params field.

input_data

The input_data field.

trans_mat

The trans_mat field.

start_stateprobs

The start_stateprobs field.

cycle_length

The cycle_length field.

absorbing

The absorbing field. If NULL, then the constructor will determine which states are absorbing automatically; non NULL values will override this behavior.

Returns

A new CohortDtstmTrans object.

---

Method sim_stateprobs()

Simulate probability of being in each health state during each model cycle.

Usage

CohortDtstmTrans$sim_stateprobs(n_cycles)

Arguments

n_cycles

The number of model cycles to simulate the model for.

Returns

An object of class stateprobs.

---

Method clone()

The objects of this class are cloneable with this method.

Usage

CohortDtstmTrans$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

See Also

create_CohortDtstmTrans() creates a CohortDtstmTrans object from either a fitted statistical model or a parameter object. A complete economic model can be implemented with the CohortDtstm class.

Examples

library("msm")
library("data.table")
set.seed(101)

# We consider two examples that have the same treatment strategies and patients.
# One model is parameterized by fitting a multi-state model with the "msm"
# package; in the second model, the parameters are entered "manually" with
# a "params_mlogit_list" object.

# MODEL SETUP
strategies <- data.table(
  strategy_id = c(1, 2, 3),
  strategy_name = c("SOC", "New 1", "New 2")
)
patients <- data.table(patient_id = 1:2)
hesim_dat <- hesim_data(
  strategies = strategies,
  patients = patients
)

# EXAMPLE #1: msm
## Fit multi-state model with panel data via msm
qinit <- rbind(
  c(0, 0.28163, 0.01239),
  c(0, 0, 0.10204),
  c(0, 0, 0)
)
fit <- msm(state_id ~ time, subject = patient_id,
           data = onc3p[patient_id %in% sample(patient_id, 100)],
           covariates = list("1-2" =~ strategy_name),
           qmatrix = qinit)

## Simulation model
transmod_data <- expand(hesim_dat)
transmod <- create_CohortDtstmTrans(fit,
                                    input_data = transmod_data,
                                    cycle_length = 1/2,
                                    fixedpars = 2,
                                    n = 2)
transmod$sim_stateprobs(n_cycles = 2)

# EXAMPLE #2: params_mlogit_list
## Input data
transmod_data[, intercept := 1]
transmod_data[, new1 := ifelse(strategy_name == "New 1", 1, 0)]
transmod_data[, new2 := ifelse(strategy_name == "New 2", 1, 0)]

## Parameters
n <- 10
transmod_params <- params_mlogit_list(
  
  ## Transitions from stable state (stable -> progression, stable -> death)
  stable = params_mlogit(
    coefs = list(
      progression = data.frame(
        intercept = rnorm(n, -0.65, .1),
        new1 = rnorm(n, log(.8), .02),
        new2 = rnorm(n, log(.7, .02))
      ),
      death = data.frame(
        intercept = rnorm(n, -3.75, .1),
        new1 = rep(0, n),
        new2 = rep(0, n)
      )
    )
  ),
  
  ## Transition from progression state (progression -> death)
  progression = params_mlogit(
    coefs = list(
      death = data.frame(
        intercept = rnorm(n, 2.45, .1),
        new1 = rep(0, n),
        new2 = rep(0, n)
      )
    )
  )
)
transmod_params

## Simulation model
tmat <- rbind(c(0, 1, 2),
              c(NA, 0, 1),
              c(NA, NA, NA))
transmod <- create_CohortDtstmTrans(transmod_params, 
                                    input_data = transmod_data,
                                    trans_mat = tmat, cycle_length = 1)
transmod$sim_stateprobs(n_cycles = 2)

# \dontshow{
  pb <- expmat(coef(fit)$baseline)[, , 1]
  
  ## From stable
  b1 <- log(pb[1, 2]/(1 - pb[1, 2] - pb[1, 3]))
  b2 <- log(pb[1, 3]/(1 - pb[1, 2] - pb[1, 3]))
  exp(b1)/(1 + exp(b1) + exp(b2))
  exp(b2)/(1 + exp(b1) + exp(b2))
  
  ### From progression
  b <- qlogis(pb[2, 2])
# }