prob_better: Calculate probabilities of comparisons of arms against with common control

Description

Used internally. This function takes a matrix as calculated by the get_draws_binom(), get_draws_norm() or a corresponding custom function (as specified using the fun_draws argument in setup_trial(); see get_draws_generic()) and a single character specifying the control arm, and calculates the probabilities of each arm being better than a common control (defined as either higher or lower than the control, as specified by the highest_is_best argument in setup_trial(), setup_trial_binom() or setup_trial_norm()). This function also calculates equivalence and futility probabilities compared to the common control arm, as specified in setup_trial(), setup_trial_binom() or setup_trial_norm(), unless equivalence_diff or futility_diff, respectively, are set to NULL (the default).

Usage

prob_better(
  m,
  control = NULL,
  highest_is_best = FALSE,
  equivalence_diff = NULL,
  futility_diff = NULL
)

Value

A named (row names corresponding to the trial arms) matrix

containing 1-3 columns: probs_better, probs_equivalence (if equivalence_diff is specified), and probs_futile (if futility_diff is specified). All columns will contain NA for the control arm.

Arguments

m: a matrix with one column per trial arm (named as the arms) and one row for each draw from the posterior distributions.
control: a single character string specifying the common control arm.
highest_is_best: single logical, specifies whether larger estimates of the outcome are favourable or not; defaults to FALSE, corresponding to, e.g., an undesirable binary outcomes (e.g., mortality) or a continuous outcome where lower numbers are preferred (e.g., hospital length of stay).
equivalence_diff: single numeric value (> 0) or NULL (default, corresponding to no equivalence assessment). If a numeric value is specified, estimated absolute differences smaller than this threshold will be considered equivalent. For designs with a common control arm, the differences between each non-control arm and the control arm is used, and for trials without a common control arm, the difference between the highest and lowest estimated outcome rates are used and the trial is only stopped for equivalence if all remaining arms are equivalent.
futility_diff: single numeric value (> 0) or NULL (default, corresponding to no futility assessment). If a numeric value is specified, estimated differences below this threshold in the beneficial direction (as specified in highest_is_best) will be considered futile when assessing futility in designs with a common control arm. If only 1 arm remains after dropping arms for futility, the trial will be stopped without declaring the last arm superior.