conjointTools

This package contains tools for designing choice based conjoint survey experiments.

Installation

The current version is not yet on CRAN, but you can install it from Github using the devtools library:

devtools::install_github("jhelvy/conjointTools")

Load the library with:

library(conjointTools)

Make experiment designs

Use the makeDoe() function to create a design of experiment

Generate a full factorial design of experiment with three attributes, each with 2 levels:

doe <- makeDoe(levels = c(2, 2, 2))
doe
#>   X1 X2 X3
#> 1  1  1  1
#> 2  2  1  1
#> 3  1  2  1
#> 4  2  2  1
#> 5  1  1  2
#> 6  2  1  2
#> 7  1  2  2
#> 8  2  2  2

You can also give your variables names based on the attributes. Here is an example of a full factorial design of experiment about apples:

doe <- makeDoe(
    levels = c(2, 2, 2),
    varNames = c("price", "type", "freshness")
)
doe
#>   price type freshness
#> 1     1    1         1
#> 2     2    1         1
#> 3     1    2         1
#> 4     2    2         1
#> 5     1    1         2
#> 6     2    1         2
#> 7     1    2         2
#> 8     2    2         2

The makeDoe() function can also generate “D”, “A”, and “I” optimal fractional factorial designs:

doe <- makeDoe(
    levels = c(2, 2, 2),
    varNames = c("price", "type", "freshness"),
    type = "D",
    nTrials = 4
)
doe
#>   price type freshness
#> 1     2    1         1
#> 2     1    2         1
#> 3     1    1         2
#> 4     2    2         2

Make coded survey designs

Once a design of experiment has been generated, a survey can be generated by sampling from the design. The design eliminates the possibility of duplicate alternatives appearing in the same choice question.

survey <- makeSurvey(
    doe       = doe,  # Design of experiment
    nResp     = 1000, # Total number of respondents (upper bound)
    nAltsPerQ = 3,    # Number of alternatives per question
    nQPerResp = 6     # Number of questions per respondent
)

dim(survey)
#> [1] 18000     7
head(survey)
#>   respID qID altID obsID price type freshness
#> 1      1   1     1     1     2    2         2
#> 2      1   1     2     1     1    2         1
#> 3      1   1     3     1     1    1         1
#> 4      1   2     1     2     1    1         2
#> 5      1   2     2     2     2    2         2
#> 6      1   2     3     2     1    2         1

The resulting data frame includes the following additional columns:

• respID: Identifies each survey respondent.
• qID: Identifies the choice question answered by the respondent.
• altID:Identifies the alternative in any one choice observation.
• obsID: Identifies each unique choice observation across all respondents.

Assess required sample sizes

To evaluate the necessary sample size to achieve a certain amount of precision about estimated model parameters, use the sampleSizer() function with the survey data frame returned from the makeSurvey() function. The function estimates a logit model on multiple subsets of the survey data frame with increasing sample sizes determined by the nbreaks argument:

results <- sampleSizer(
    survey   = survey,
    parNames = c('price', 'type', 'freshness'),
    parTypes = c('c', 'd', 'd'), # Set continuous vs. discrete variables
    interactions = TRUE, # Add interactions between each attribute
    nbreaks  = 10
)

# Preview results
head(results)
#>   size        se               coef
#> 1  100 0.1611530              price
#> 2  100 0.3110412             type_2
#> 3  100 0.3118941        freshness_2
#> 4  100 0.1897302       price*type_2
#> 5  100 0.1887158  price*freshness_2
#> 6  100 0.1891048 type_2*freshness_2

View a plot of the results

library(ggplot2)
ggplot(results) +
    geom_point(aes(x = size, y = se, color = coef),
               fill = "white", pch = 21) +
    scale_y_continuous(limits = c(0, NA)) +
    labs(x = 'Number of observations',
         y = 'Standard Error',
         color = "Variable") +
    theme_bw()

Version and License Information

• Date First Written: October 23, 2020
• Most Recent Update: December 09 2020
• License: MIT
• Latest Release: 0.0.2

Citation Information

If you use this package for in a publication, we would greatly appreciate it if you cited it - you can get a bibtex citation entry with citation("conjointTools"):

citation("conjointTools")
#> 
#> To cite conjointTools in publications use:
#> 
#>   John Paul Helveston, Martin Lukac, Alberto Stefanelli (2020).
#>   conjointTools: Tools For Designing Conjoint Survey Experiments.
#> 
#> A BibTeX entry for LaTeX users is
#> 
#>   @Manual{,
#>     title = {conjointTools: Tools For Designing Conjoint Survey Experiments},
#>     author = {John Paul Helveston and Martin Lukac and Alberto Stefanelli},
#>     year = {2020},
#>     note = {R package version 0.0.2},
#>     url = {https://jhelvy.github.io/conjointTools/},
#>   }