JSmediation is an R package aiming to provide a set of functions to conduct mediation analysis joint-significance tests. The goal of JSmediation is to provide a consistent syntax to conduct joint-significance tests.

This is motivated by the fact that joint-significance tests perform better in terms of false positive rate control than other tests like bootstrap-based methods (Yzerbyt, Muller, Batailler, & Judd, 2018). To do so, it provides a family of mdt_* functions helping one conducting different mediation analysis.

Current implemented models are:

• simple mediation (mdt_simple)
• within-participant mediation (mdt_within, but see also mdt_within_wide)
• moderated mediation (mdt_moderated)

Every mdt_* functions take at least four arguments: data (the data frame containing the data to be used),IV (the unquoted column name of the independent variable in the data frame), DV (the unquoted column name of the dependent variable in the data frame), and M (the unquoted column name of the mediator in the data frame).

## Installation

You can install the released version of JSmediation from CRAN with:

install.packages("JSmediation")

You can install the development version from GitHub with:

# install.packages("devtools")
devtools::install_github("cedricbatailler/JSmediation", build_vignettes = TRUE)

## How to use JSmediation

library(JSmediation)

The JSmediation package contains several functions as well as example data sets that can be used as an example. The ho_et_al data set comes from Ho et al. (2017; Exp. 3) and contains variables to test a simple mediation. As a simple example, we will conduct a joint-significance test of the indirect effect of discrimination on hypodescent passing by linked fate.

We will first recode condition variable which is a character to a contrast code using the build_contrast function.

data("ho_et_al")

ho_et_al$condition_c <- build_contrast(ho_et_al$condition,
"High discrimination",
"Low discrimination")

head(ho_et_al)
#>   id           condition    sdo linkedfate hypodescent condition_c
#> 1  2  Low discrimination 1.8125      6.000    2.333333         0.5
#> 2  3 High discrimination 1.5625      5.875    6.000000        -0.5
#> 3  4 High discrimination 1.7500      6.625    6.000000        -0.5
#> 4  5  Low discrimination 4.2500      5.125    5.666667         0.5
#> 5  6  Low discrimination 1.9375      4.375    4.000000         0.5
#> 6  9 High discrimination 2.8750      3.750    4.000000        -0.5

Now, we can conduct a joint significant test using the mdt_simple function.

JS_model <- mdt_simple(ho_et_al,
DV = hypodescent,
IV = condition_c,
M  = linkedfate)

JS_model
#> Test of mediation (simple mediation)
#> ==============================================
#>
#> Variables:
#>
#> - IV: condition_c
#> - DV: hypodescent
#> - M: linkedfate
#>
#> Paths:
#>
#> ====  ==============  =====  =======================
#> Path  Point estimate     SE  APA
#> ====  ==============  =====  =======================
#> a             -0.772  0.085  t(822) = 9.10, p < .001
#> b              0.187  0.033  t(821) = 5.75, p < .001
#> c             -0.171  0.081  t(822) = 2.13, p = .034
#> c'            -0.027  0.083  t(821) = 0.33, p = .742
#> ====  ==============  =====  =======================
#>
#> Indirect effect index:
#>
#> Indirect effect index is not computed by default.
#> Please use add_index() to compute it.
#>
#> Fitted models:
#>
#> - X -> Y
#> - X -> M
#> - X + M -> Y

One will have to make sure that both a and b are significant to conclude that there is a mediation pattern.

### References

Yzerbyt, V., Muller, D., Batailler, C., & Judd, C. M. (2018). New recommendations for testing indirect effects in mediational models: The need to report and test component paths. Journal of Personality and Social Psychology, 115(6), 929–943. doi: 10.1037/pspa0000132

Ho, A. K., Kteily, N. S., & Chen, J. M. (2017). “You’re one of us”: Black Americans’ use of hypodescent and its association with egalitarianism. Journal of Personality and Social Psychology, 113(5), 753-768. doi: 10.1037/pspi0000107

## Contributing

Contributions are absolutely welcome. Please note that this project is released with a Contributor Code of Conduct.

By participating in this project you agree to abide by its terms.