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The Data Dictionary is a spreadsheet in CSV format representing the structure of your instrument database. Your Data Dictionary contains the metadata used to construct your data collection instruments. It captures the same information as the Online Designer, but displays it in a more concise format.
Each row in a Data Dictionary spreadsheet corresponds to a field in your data entry form. The order of questions in a Data Dictionary file defines the order they appear in the database.
You can use the Data Dictionary to change the structure of your data collection instruments.

• Changes you make with the Data Dictionary are not propagated in real time to your project; changes are not committed until you upload the modified Data Dictionary file.

• Changes for development databases will take effect immediately, but changes to production databases will need to be reviewed and approved by the REDCap administrator before they take effect. The new structure will apply to both new and existing records.

Once your project is in Production you can make changes using the Data Dictionary. However, there are potential data loss ramifications. Take precaution by saving a copy of your project data so it can be retrieved in the case of data loss.

The REDCap project will store backup copies of previous data dictionaries in case a reversion is needed; but it does not store backup copies of project data.

which provides a

detailed chart of

the impact specific changes will have on your project. This is relevant to users whose project is in Production

mode where real data collection has begun.

Commonly requested changes and considerations to be mindful of:

Deletion of Field annotations:
Different consequences result depending upon the action tag being modified.  For example:

• If you remove the @DEFAULT action tag, this will not affect any existing data that has been saved (i.e. the instrument was opened either in survey mode and submitted, or in data entry mode and marked "saved" when exiting).

• If  @hidden-survey is removed, questions will show in survey instruments

• There are far too many action tags to be able to list  the impact of data dictionary changes in this article.  Think through what the action tag does and possible ramifications. Always export your data for retrieval purposes

Changing Field Calculations:

• Changing field calculations is a bit tricky, but as long as you do not modify the fields included in the calculation, you can always revert the calculation back. If you have existing saved data for a calculation on certain records, and then change the calculation, the existing saved data will not reflect the new calculation unless you open that record, open the instrument, and allow redcap to re-calculate.

Branching Logic Changes:

• Branching logic changes are also tricky.

  • If you'd like to remove branching logic from a question, this action will not affect any data.

  • If you'd like to add new branching logic to a question, you'll want to think about if that question has existing data for existing records. If so, assure your existing records will meet the new logic, otherwise their data will be at risk for deletion. If you determine the existing records will not meet the new logic, then we recommend you download existing data before submitting new logic.

  • If you'd like to modify existing logic, you'll also need to consider if there are existing data for existing records that may not meet the new logic.

Changing field types:

• Changing from radio<>dropdown is fine.

• Changing from radio/dropdown<>checkbox is not fine because data results are stored differently.

• Changing from calculation<>text will delete data.

• Changing from text>note is fine, but note>text may delete data via truncation

• .

Changing variable names (rename a field)

• This will simply create a new field with the new name and the old field will no longer exist (and neither will the data). Do not do this!

Renaming the instrument

• Don't use data dictionary to rename the instrument name. The instrument status data will be lost if using data dictionary to rename the instrument. Instead, you can rename the instrument in the Online Designer.