How do I know when a variable was first added to the questionnaire & if it has changed over the years?

Date of addition

Variables that are recent additions to a survey are marked with a date in brackets to show when data first became available. For example, a question with the data [07/08] was first released in July 2008. Questions or variables that are changed are treated as new if the change causes a shift in data. Software trending tools only recognise variables that are constant across surveys and will not trend beyond the point at which a variable was added or treated as new.