randomizr (version 2.0.1)

cluster_ra_probabilities: Probabilities of assignment: Cluster Random Assignment

Description

Returns the probability that each unit is assigned to each condition under cluster random assignment. Every unit in a cluster shares its cluster's probability, since clusters move together.

Usage

cluster_ra_probabilities(
  clusters = NULL,
  m = NULL,
  m_unit = NULL,
  m_each = NULL,
  prob = NULL,
  prob_unit = NULL,
  prob_each = NULL,
  num_arms = NULL,
  conditions = NULL,
  simple = FALSE,
  check_inputs = TRUE
)

Value

A matrix with N rows and one column per treatment condition, with columns named prob_<condition>. Entry (i, j) is the probability that unit i is assigned to condition j, and every row sums to 1.

Arguments

clusters

A vector of length N indicating which cluster each unit belongs to. (required)

m

Use for a two-arm design in which exactly m clusters are assigned to treatment. (optional)

m_unit

Use for a two-arm design. unique(m_unit) clusters are assigned to treatment; must be the same for all units and of length N. (optional)

m_each

Use for a multi-arm design. A numeric vector giving the number of clusters assigned to each condition; must sum to the total number of clusters. (optional)

prob

Use for a two-arm design in which either floor(N_clusters*prob) or ceiling(N_clusters*prob) clusters are assigned to treatment. Which of the two is used is itself random: the ceiling is drawn with probability equal to the fractional part of N_clusters*prob and the floor otherwise, so that each cluster's probability of assignment is exactly prob. When N_clusters*prob is a whole number the count is fixed. Must be between 0 and 1. (optional)

prob_unit

Use for a two-arm design. unique(prob_unit) will be passed to the prob argument and must be the same for all units. (optional)

prob_each

Use for a multi-arm design. A numeric vector giving the probability of assignment to each condition; entries must be nonnegative, sum to 1. Because of integer rounding, the exact number of clusters assigned to each condition may differ slightly from assignment to assignment, but the overall probability of assignment is exactly prob_each. (optional)

num_arms

The total number of treatment arms. If unspecified, determined from m_each or conditions. (optional)

conditions

A character vector giving the names of the treatment groups. If unspecified, groups will be named T1, T2, T3, etc. (optional)

simple

Logical, defaults to FALSE. If TRUE, clusters are assigned to conditions independently (simple random assignment at the cluster level), so the number of treated clusters varies from draw to draw. Do not specify m or m_each when simple = TRUE. (optional)

check_inputs

Logical. Whether to verify before assigning that the arguments are internally consistent: that counts sum to the number of clusters, that probabilities lie between 0 and 1 and sum to 1, and so on. Defaults to TRUE. FALSE skips the checking only: num_arms and conditions are still derived from the other arguments, so the same call draws the same assignment either way. What goes is the verification, and an impossible design is then no longer refused. block_m larger than a block, for instance, quietly treats the whole block. Declaring the design once with declare_ra() and drawing from it with conduct_ra() is the usual way to avoid re-checking the same arguments in a simulation. (optional)

Details

These are the quantities inverse-probability weights are built from: weight each unit by the reciprocal of the probability of the condition it landed in, which obtain_condition_probabilities() extracts for you.

See Also

cluster_ra()

Examples

# Two Group Designs
clusters <- rep(letters[1:10], times = 1:10)
prob_mat <- cluster_ra_probabilities(clusters = clusters)
head(prob_mat)

prob_mat <- cluster_ra_probabilities(clusters = clusters, m = 4)
head(prob_mat)

prob_mat <- cluster_ra_probabilities(clusters = clusters,
                                     m_each = c(6, 4),
                                     conditions = c("control", "treatment"))

# Multi-arm Designs
prob_mat <- cluster_ra_probabilities(clusters = clusters, num_arms = 3)
head(prob_mat)

prob_mat <- cluster_ra_probabilities(clusters = clusters, m_each = c(3, 3, 4))
head(prob_mat)

prob_mat <- cluster_ra_probabilities(clusters = clusters, m_each = c(3, 3, 4),
                         conditions = c("control", "placebo", "treatment"))
head(prob_mat)

prob_mat <- cluster_ra_probabilities(clusters = clusters,
                         conditions = c("control", "placebo", "treatment"))
head(prob_mat)

prob_mat <- cluster_ra_probabilities(clusters = clusters,
                                     prob_each = c(0.1, 0.2, 0.7))
head(prob_mat)