WHO performs the Rasch Analysis for the Model Disability Survey using
the software `R`

. `R`

is an open source,
statistical programming software. How to program in `R`

is
beyond the scope of this guide. However the codes we will discuss as
follows have been written in such a way to require minimal programming
knowledge, and this guide tries to make the instructions for how to use
them as simple as possible.

To learn about `R`

, please see the references provided at
the end of this guide.

To use the package provided by WHO, `R`

must be installed
from the Comprehensive R Archive
Network (CRAN). We also recommend installing RStudio, a
very popular integrated development environment (IDE), for
`R`

. One can think of the relationship between `R`

and `RStudio`

like a car: `R`

is the engine of the
car, while `RStudio`

is the dashboard and controls.
`RStudio`

cannot be run without `R`

, but it makes
`R`

easier to use. Both are free to install and use
indefinitely.

A “package” is a collection of `R`

functions, data and
code with a specific purpose and in a well-defined format. There are
thousands of packages for `R`

that have been written by
`R`

users. People write packages in order to share codes they
have written that make specific tasks easier. WHO has written a package
in order to make analysis of the data from the MDS easier. The package
written by WHO is called `whomds`

. To install the package,
run the following code in the console:

`install.packages("whomds")`

`whomds`

Once `whomds`

is installed, it can be opened with the
following code:

`library(whomds)`

`whomds`

contains three kinds of functions:

`table_*()`

functions - produce different fit-for-purpose tables`fig_*()`

functions - produce different fit-for-purpose figures`rasch_*()`

functions - used when performing Rasch Analysis

In this section we will focus on the `rasch_*()`

functions.

There are two sets of `rasch_*()`

functions in the
`whomds`

package: one set for adults, and one set for
children. The reason different functions are needed for each group is
that the type of Rasch Analysis performed for each group is different.
The Rasch Analysis performed for adults is straightforward; the whole
adult population can be considered in one group. The Rasch Analysis for
children requires a more complicated analysis, because children at
different ages are very different, and they can perform vastly different
types of activities. First we will describe the analysis of adults, and
then describe the analysis of children.

The package `whomds`

depends on several other packages to
run properly. When `whomds`

is installed, all of the other
packages it uses will also be installed. Be sure that these other
packages are installed correctly by investigating any errors that arise
during installation.

The additional packages are:

`colorspace`

`dplyr`

`eRm`

`ggraph`

`ggplot2`

`GPArotation`

`grDevices`

`igraph`

`nFactors`

`plyr`

`polycor`

`purrr`

`RColorBrewer`

`readr`

`rlang`

`scales`

`srvyr`

`stringr`

`TAM`

`tibble`

`tidygraph`

`tidyr`

`WrightMap`