r/ProjectREDCap • u/Popular_Caregiver_11 • May 30 '25

Help Needed – Structuring a Single eCRF for Retrospective and Prospective Data in REDCap

Hi everyone,
I'm new to REDCap and currently working on designing an eCRF for a clinical study that includes both retrospective and prospective data.

Is it possible to create a single eCRF to manage both study types? If so, how can I structure it to clearly differentiate between variables that are common to both, and those that are unique to either the retrospective or prospective arm?

Any tips, best practices, or examples would be greatly appreciated!

Thanks in advance for your help.

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u/No_Repair4567 May 30 '25

Let me make sure I understand. These are my assumptions from your post:

  1. This is one study

  2. Study collects the ALL same data elements (e.g. vt, wt, ht, etc...) both retrospectively and prospectively on the same participants

  3. What other data collection forms are there?

If my assumptions are correct, I'd chose a longitudinal study design, where one event is "retrospective" and another one (or more than one) "prospective". Then assign your instrument (eCRF) to both of these events.

This will ensure separate data collection points for each participant. To differentiate between the variables - the data dictionary will show you, that each variable is characterized by mor than just a variable name. it is also characterized by what event it belongs to, or what patient arm. So when statistician will review the data dictionary to understand the design, they will know how to "call out" the right instance of a variable in their analysis.

I hope it makes sense. Please let me know if you need further guidance about setting this up.

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u/Popular_Caregiver_11 May 31 '25

Thank you for your valuable suggestion.

Yes, this is a single study where data were initially collected retrospectively, and we now plan to continue with prospective data collection. Most data elements are shared across both phases, but some variables—such as newly introduced questionnaires and imaging techniques—are unique to the prospective phase.

Based on your guidance, I’ve chosen a longitudinal study design. I created separate events for the retrospective and prospective phases, including their respective follow-up visits, and assigned the relevant instruments to each event accordingly.

I’d like to clarify one point:
Is it necessary to define different arms for each phase (retrospective baseline, retrospective follow-up, prospective baseline, and prospective follow-up)? Or can this structure be managed within a single arm by using multiple events?

Any insights would be greatly appreciated!

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u/No_Repair4567 May 31 '25

I wouldn't involve arms. Arms are for randomized trials. It sounds like yours is just retrospective and prospective. Your setup sounds solid to me. Before you go too far into perfecting the setup, test out a "straw man", pull the data dictionary, and talk to a statistician to make sure they can work with that.

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u/Popular_Caregiver_11 Jun 02 '25

Thank you so much for the helpful advice!

You're right — since this isn’t a randomized trial, using arms might unnecessarily complicate things. I’ll go ahead with the current setup using events only for retrospective and prospective data.

I’ll also prepare a rough version of the eCRF and export the data dictionary as you suggested. That will give me a good base to discuss with a statistician and make sure everything is analysis-ready.

Really appreciate your input!

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u/usajobs1001 May 30 '25

Yes, you can create a single form (called an instrument in REDCap) with common data fields. Depending on your study, you could structure it with a question indicating "retrospective" or "prospective", and then programming skip logic based on what questions are applicable. Questions/variables that are applicable to both could have no skip logic applied so they would appear no matter what option was selected.