ARC Special Field Types Documentation

This document provides a detailed explanation of the special field types used within the ISARIC ARC (Analysis and Research Compendium) framework to support dynamic, reusable, and semantically structured Case Report Forms (CRFs). These field types extend beyond standard REDCap functionality to enable complex logic, repeated entries, hierarchical lists, and units management.

Overview: REDCap-Compatible Extensions

Most fields in ARC use standard REDCap field types such as text, radio, checkbox, dropdown, calc, and notes. However, to support enhanced functionality and automation, ARC introduces several special field types:

  • user_list

  • list

  • multi_list

  • Blank field (select units in Question)

These are interpreted and transformed into REDCap-compatible fields when generating a data dictionary.

1. user_list

Description

A is a structured field type that references a predefined list of options from an external file, where the user has marked some values as selected or preset_ (i.e., shown as default radio options) and others as optional extensions. A user_list is a structured field type that references a predefined list of options from an external file, which the user can modify to include the pertinent options for their particular context. This links to specific functionality in ISARIC BRIDGE, where users can select the options they wish to include for a given question. Additionally, each version of ARC includes pre-selected options in the form of presets, which are shown by default, while other options remain available as optional extensions.

Example

Variable: inclu_disease
List source: Lists/inclusion/Diseases.csv

BRIDGE Transformation

  • radio field with checked values as options: if the number of checked values < 15

  • dropdown field with checked values as options: if the number of checked values >= 15

  • dropdown (otherl2) to show extended values if user selects “Other”

  • text field (otherl3) to specify unlisted values

Derived Variables

  • inclu_disease_otherl2

  • inclu_disease_otherl3

2. list

Description

list is used for fields that support multiple repeated selections from a predefined value set. Like user_list, the options for list fields are loaded from external CSV files in the ARC GitHub repository.

Example

Variable: comor_unlisted
List source: Lists/conditions/Comorbidities.csv

BRIDGE Transformation

  • Multiple dropdown entries: 0item, 1item, …, nitem

  • Each followed by:

    • text field for “Other” entries: 0otherl2, etc.

    • radio field asking if there’s an additional entry: 0addi, etc.

Derived Variables

  • comor_unlisted_0item, comor_unlisted_1item, …

  • comor_unlisted_0otherl2

  • comor_unlisted_0addi

3. multi_list

Description

multi_list represents a multiselect list where several options can be checked simultaneously. Like user_list, its options are also loaded from external CSV files.

Example

Variable: demog_race
List source: Lists/demographics/Race.csv

BRIDGE Transformation

  • A checkbox group with selected options

  • If value 88 (Other) is selected:

    • Show dropdown with less common values (otherl2)

    • Show text field for specification (otherl3)

Derived Variables

  • demog_race: base checkbox

  • demog_race_otherl2, demog_race_otherl3

4. select units

Description

This is a structural pattern rather than an explicit type. It applies to clinical measurements (e.g., height, weight, temperature) that may be recorded in more than one unit (e.g., cm/in, kg/lb, °C/°F). The core variable usually includes “(select units)” in its question text and is linked to two or more variants defined with specific units tha share the same prefix.

Example

  • Base question: demog_height → “Height (select units)”

  • Variants:

    • demog_height_cm: numeric field in centimeters

    • demog_height_in: numeric field in inches

  • Base question: demog_weight → “Weight (select units)”

  • Variants:

    • demog_weight_kg: numeric field in kilograms

    • demog_weight_lb: numeric field in pounds

BRIDGE Transformation

  • A unified text field (e.g., demog_height) for the value

  • A companion radio field (e.g., demog_height_units) to select which unit is used

Derived Variables

  • demog_height: unified height input

  • demog_height_units: unit selector (e.g., cm/in)

  • demog_weight: unified weight input

  • demog_weight_units: unit selector (e.g., kg/lb)

This approach reduces redundancy, improves clarity, and ensures that unit selection is explicit and standardized.

Moreover, this design enables CRF customization in ISARIC BRIDGE: users can choose which unit(s) to display when configuring the form for a specific data collection setting. This allows alignment with local clinical practices (e.g., countries preferring cm/in or kg/lb) while maintaining a unified structure in the backend.

Visual Summary

Below is a simplified flowchart of how each ARC type expands into REDCap-compatible fields:

user_list
  └── radio field (Selected options) if Selected options < 15
  └── dropdown field (Selected options) if Selected options >= 15
      └── dropdown (Other options)
          └── text (Specify other)

list
  └── dropdown_0item
      ├── text_0otherl2
      └── radio_0addi

multi_list
  └── checkbox (main options)
      ├── dropdown_otherl2
      └── text_otherl3

select units
  ├── text (numeric value)
  └── radio (unit selector)

Notes

  • Lists are stored in the ARC GitHub repo under /Lists/…

  • The transformation is handled automatically during CRF genration from ISARIC BRIDGE

  • These structures support modular, scalable, and interoperable CRFs