The R package instrument is an item response theory modeling software whose purpose is:

• Fit a variety of IRT models including the univdimensional, multidimensional, and higher-order models
• Specify regression models in the context of IRT with both fixed and random effects (i.e., mixed modeling)
• Simple model syntax to describe IRT models with and without regression

• The instrument R package source code can be found at github.com/inirt/theta2

• Full documentation and tutorials can be found at inirt.github.io/doc/

1. Since this is an R pacakge, the user first needs to install R from the R project website.

2. In addition to R, a good editor is recommended such as RStudio.

3. The key dependency of this package is RStan. Use the development version of the software, which can be installed with:

install.packages("rstan", repos = c("https://mc-stan.org/r-packages/", getOption("repos")))

4. Once R and RStan are installed, open an R console and install the package from Github using remotes (recommended):

# remotes
install.packages("remotes")
# install from Github
remotes::install_github("Rinstrument/instrument")

Alternatively, install from CRAN with (coming soon):

install.packages("instrument")