Variables in Draco are arrays of values representing data in the main
data set. The variables are displayed in the Data Window. Variables can also have
"missing" values within their array, representing blank data points
without specification at certain points within the data set.
Because all variables have multiple values, variables are organized into
rows across the data set. Therefore, when writing an equation in one of
the many dialogs which require this user input, the equations containing
variables are evaluated at each row separately using only variable
values falling on the specific row. If a row is ever referred to that
contains a "missing" value in on of the equation's variables, the
result of the equation evaluation will also be "missing."
If the user wishes to represent a value that does not change across the
data set, the Constant data type is more
appropriate.