Blocks: Create blocks (sub-designs) from a given design.

In idefix: Efficient Designs for Discrete Choice Experiments

Create blocks (sub-designs) from a given design.

Description

This function breaks down a design output from Modfed or CEA into a specified number of blocks while aiming to maintain balance in levels frequency across the resulting blocks.

Usage

Blocks(
  des,
  n.blocks,
  n.alts,
  blocking.iter = 50,
  no.choice = FALSE,
  alt.cte = NULL
)

Arguments

des	The design to be distributed into blocks (sub-designs).
n.blocks	A numeric value indicating the desired number of blocks to create out of the provided design.
n.alts	The number of alternatives in each choice set.
blocking.iter	A numeric value indicating the maximum number of iterations for optimising the level balance in the blocks. The default value is 50.
no.choice	A logical value indicating whether a no choice alternative is added to each choice set in the provided design. The default is FALSE.
alt.cte	A binary vector indicating for each alternative whether an alternative specific constant is present in the design. The default is NULL.

Details

The argument n.blocks specifies the number of blocks to create. The algorithm strives to distribute the choice sets of the design evenly among the blocks, while maintaining level balance across them. The choice sets are assigned sequentially to the blocks, aiming to maintain the closest possible level balance among them up to that stage in the sequence. Hence, the algorithm runs different iterations, during each of which the choice sets in the design are shuffled randomly. The argument blocking.iter specifies the maximum number of these iterations.

If the design has a no.choice alternative then no.choice should be set to TRUE. Additionally, asc.col should indicate the number of alternative specific constants that are included in the design, if any.

This functionality is also available as an argument (n.blocks) when creating an efficient design using Modfed or CEA.

Note: To make sure the code works well, the names of the variables in the provided design should be aligned with variable names that the function Profiles produces. For example, if attribute 1 is a dummy variable of 3 levels then its corresponding columns should have numbered names such as: var11 and var12, or (if labelled) price1 and price2, for instance.

Value

A list of blocks from the original design is returned. Additionally, the frequency of every level in each block is returned.

Examples

# DB-efficient designs
# 3 Attributes with 3 levels, all dummy coded. 1 alternative specific constant = 7 parameters
cand.set <- Profiles(lvls = c(3, 3, 3), coding = c("D", "D", "D"))
mu <- c(0.5, 0.8, 0.2, -0.3, -1.2, 1.6, 2.2) # Prior parameter vector
v <- diag(length(mu)) # Prior variance.
set.seed(123) 
pd <- MASS::mvrnorm(n = 10, mu = mu, Sigma = v) # 10 draws.
p.d <- list(matrix(pd[,1], ncol = 1), pd[,2:7])
design <- Modfed(cand.set = cand.set, n.sets = 8, n.alts = 2, 
       alt.cte = c(1, 0), parallel = FALSE, par.draws = p.d)
Blocks(design$BestDesign$design, n.blocks = 2, n.alts = 2, alt.cte = c(1, 0))

idefix documentation built on April 4, 2025, 1:51 a.m.