Each field within an instrument requires a 'Variable Name'. It is entered in the box highlighted below of the 'Add Field' pop up.
Variable names usually begin with the instrument that they are in, for instance, the example above is from the eligibility instrument so has been given 'elig' as the beginning of the variable name.
Usually the keyword(s) from the 'Field Label' are included and these are separated by an underscore as spaces cannot be used. This gives the variable name 'elig_participantid'.
Variable names are not displayed during data entry.