Create an object evpi_decrease

Description

An object that combines three others objects : object_inmb, object_pop, object_var_inmb. It contains methods to compute the value of perfect information (EVPI) that would remain after a study of n participants (EVPIn). For each additional individual included, the EVPI decreases. So EVPIn is a decreasing vector. It is used to determine the optimal sample size.

Usage

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create_object_evpi_decrease(object_inmb, object_pop, object_var_inmb,
  step_exp = 1, step_ref = 1)

Arguments

object_inmb

: an object that represents the INMB (Incremental Net Monetary Benefit) Create an object with one of these functions : create_object_inmb_direct, create_object_inmb

object_pop

: an object that represents the size of the targeted population. Create an object with create_object_pop

object_var_inmb

: an object that represents the variance of INMB. The variance of INMB can be directly hypothesized, or calculated through sdc, sde, rho and lambda, or calculated through sdc_ref, sde_ref, sdc_exp, sde_exp, rho and lambda. Create an object with one of these functions : create_object_var_inmb_direct, create_object_var_inmb,create_object_var_inmb_diff

step_exp

(default=1) : the minimal number of individuals to be included in the experimental group to respect the allocation ratio. If the allocation ratio is 2:1 in favor of the experimental group, step_exp=2 and step_ref=1.

step_ref

(default=1) : the minimal number of individuals to be included in the reference group to respect the allocation ratio. If the allocation ratio is 2:1 in favor of the reference group, step_ref=2 and step_exp=1.

Value

create_object_evpi_decrease returns an object of class EVPI_DECREASE

Examples

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## First, create 3 objects : inmb, pop and var_inmb, then create the evpi_decrease object
object_lambda <- create_object_lambda (20000)
object_inmb <- create_object_inmb(de = 0.04, dc=-168, object_lambda = object_lambda)
object_var_inmb <- create_object_var_inmb(sde=0.12, sdc=2100, rho=0.1, object_lambda=object_lambda)
object_pop <- create_object_pop(horizon = 20, discount=0.04, N_year = 52000)
object_evpi_decrease <- create_object_evpi_decrease(object_inmb, object_pop, object_var_inmb)