Identifiers
The goal of this article is to assist users in understanding the different types of identifiers: Anchor
Note: this feature should be enabled before you start collecting real data. That is because if you are already collecting real data and there are duplicates in your project, you cannot enable this feature. It is not possible to specify that the combination of two or more fields be unique.
Initial Considerations
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This article reviews the below topics related to Record keeping
To see these in action, expand the topic below that you wish to review |
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Unique Identifier
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The unique identifier must be a 'text' field. Unique identifier values will be visible at the end of the URL – and likely cached in web browsers – as individual records are viewed or entered.
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The below example show cases a Data Entry form as the first instrument in a project, where the unique identifier has been updated from ‘record_id’ to ‘study_id’  If you wish the edit this field, note the below:
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Auto-Numbering of Records & how to disable
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When your first data collection instrument is enabled as a survey, auto-numbering is mandatory for the project. If you plan to manually enter your unique identifier and wish disable auto-numbering, follow the below instructions. To disable auto-numbering, follow the below steps: NOTE: This can only be disabled when your project is in Development mode.
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Custom Record Label
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Custom Record Label may be used to display a specified field next to the record number. For example you may choose to display a participants name to ensure you are selecting the right record. You may append other data and/or static text to any record name (e.g., Study ID) as the record is displayed on your data collection instruments, such as inside the drop-down lists when choosing a record and at the top of the page after being selected. Simply provide the text you wish to display below, and place any variable names inside square brackets [ ], after which the data collected for those variables for that record will replace the variable in the text. To create a custom record label, follow the below steps:
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Secondary Unique field
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The data values entered into the (optional) secondary unique field must be unique. Unlike the value of the primary unique identifier field, |
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this will not be |
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visible in a URL. |
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You may designate a text field to serve as a unique constraint whose value cannot be duplicated or shared by any other record in the project. When a value is entered or imported for the secondary unique field, it will be checked in real time to ensure it is not shared by another record, and if so, will ask the user to enter another value. This means that if a participant is completing a survey for a second time in which this feature is enabled, they will see the following pop-up box: 
To enable a Secondary Unique field, follow the below steps:
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Frequently Asked Questions
Q: If the unique identifier is arbitrary to me, can the system auto-assign a unique value to each of my records?
Yes. You can enable auto-numbering for naming new project records on the Project Setup > Enable optional modules and customizations page. This option will remove the ability for users to name new records manually and will instead provide a link that will auto-generate a new unique record value. The value is numeric and increments from the highest numeric record value in the project. If no records exist, it will begin with '1'.
Q: How can I set the default auto-numbering to start at a particular number such as 2000?
You can disable auto-numbering and add the first record using the ID number as the start value. Once this record is saved, you can enable the auto-numbering customization, so subsequent records will be created starting after 2000.
Q: What's the difference between the unique identifier, secondary unique identifier and the redcap_survey_identifier?
The first variable listed in your project is the unique identifier which links all data for a record.
The secondary unique field allows you to identify another unique identifying value of the field (e.g, name, subject
#, ). It will also appear at the top of the data entry page when viewing a record/response. Unlike the value of the primary unique identifier field, it will not be visible in the URL.number).
The redcap_survey_identifier is the identifier defined for surveys when utilizing the Participant Email Contact List and sending survey invitations from the system. The "Participant Identifier" is an optional field you can use to identify individual survey responses so that the participant doesn't have to enter any identifying information into the actual survey. This field is exported in the data set; the email address of the participant is not.
Q: If we wanted to get rid of our own IDs and just use auto-numbering, could we start at, say, 3000?
If you wanted to start the auto-numbering record ID at 3000, you would have to go in to an existing record (it is best to create a fake record to do this) and manually change the record number to 2999 so that the next assigned record # would be 3000. You will need to have "Rename Records" ability under your User Rights in order to do this. The hard stop rule for auto numbering is that it can't be done if you have a public survey. If the project has a public survey it has to have auto numbering.
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- A field in addition to the primary record identifier for which REDCap will ensure the uniqueness of all values
- Values will also be included alongside the primary record identifier in the record selection lists
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More info: Participant Identifier