Longitudinal Project Design

REDCap Longitudinal Projects Guide

Longitudinal projects in REDCap allow you to collect data across multiple time points, visits, or repeated occurrences for the same participant.

This structure is ideal for studies involving follow-up visits, repeated measures, or ongoing participant tracking.

Core Concept: One Record → Multiple Events → Repeated Data Over Time
Important: Longitudinal structure should be enabled before production whenever possible. Converting after data collection has begun can be complex and may impact existing data.

When to Use Longitudinal Design

  • Multiple visits (baseline, follow-up, discharge)
  • Repeated measures over time
  • Ongoing participant tracking
  • Data collected at scheduled intervals
Best practice: Use longitudinal design when the same participant has multiple time-based data points—not for grouping different participant types.

Enable Longitudinal Mode

Enable longitudinal data collection in Project Setup → Additional Customizations.

Once enabled, you will define events and assign instruments accordingly.

Best practice: Enable this early in development. Structural changes later are more complex and require careful review.

Define Events

Events represent time points or visits in your study.

  • Baseline
  • Visit 1, Visit 2, Visit 3
  • Follow-up (e.g., 30-day, 6-month)
  • Ad hoc or unscheduled visits
Best practice: Name events clearly and consistently to reflect real study workflows.

Use Arms (When Needed)

Arms are used to separate different study groups or workflows.

  • Treatment vs Control groups
  • Different study cohorts
  • Distinct protocols within one project
Important: Do not use arms simply to separate survey types or user groups. This often creates unnecessary complexity.

Assign Instruments to Events

Each instrument must be mapped to the appropriate event(s).

  • Baseline forms → Baseline event
  • Follow-up surveys → Follow-up events
  • Shared instruments → Multiple events
Best practice: Map only what is needed per event to keep data entry clean and intuitive.

Repeating Events & Instruments

Repeating functionality allows multiple entries within the same event.

  • Repeating instruments (e.g., medications, adverse events)
  • Repeating events (e.g., multiple unscheduled visits)
Best practice: Use repeating instruments for lists and repeating events for full visit-level duplication.

Surveys in Longitudinal Projects

Surveys can be enabled per instrument and tied to specific events.

  • Use Survey Queue for sequencing
  • Use Automated Invitations for timing
  • Use logic to control survey availability
Important: REDCap supports only one public survey link per project. Use Survey Queue and logic to direct participants appropriately.

Design Best Practices

  • Align events with real-world workflow
  • Keep naming consistent (Visit 1, Visit 2, etc.)
  • Minimize unnecessary arms
  • Use repeating instruments thoughtfully
  • Test full participant flow across all events
  • Use clear form and event descriptions
Best practice: Build for usability first—complex designs increase data entry errors and user confusion.

Common Pitfalls

  • Using arms instead of events
  • Overcomplicating event structure
  • Mapping all instruments to all events unnecessarily
  • Not testing full workflows
  • Converting to longitudinal after production
Important: Most longitudinal issues stem from overengineering. Keep the structure as simple as possible.

Additional Resources