---
title: Choosing a study design
description: Choose whether a study follows use, compares units or compares groups, and where it runs.
updated: 2026-10-29
---

> All VIABLE docs, for people and their agents: https://developers.viablelab.org/llms.txt

# Choosing a study design

Choose the kind of study by what changes for learners.

| What changes for learners | Choose | The study is |
| --- | --- | --- |
| Nothing: you follow how a class uses a course, or how visitors use a chat page | **Follow how it is used** | Observational, with no conditions |
| The same learners have the AI in some units and not others, or one agent and then another | **Compare units, with the same learners** | Comparative, comparing units: one plan, or two orders drawn at random |
| Learners or whole classes get different versions | **Compare groups of learners** | Comparative, comparing groups: each learner or section gets one condition |

Two orders keep a unit's content or time of year from deciding the result. Observational or comparative is fixed when you create the study. What a comparative study compares can change on **Design** until it opens.

## Common designs

- RCT: comparing groups, **With AI** and **Without AI**, each person at random.
- Cluster randomized: comparing groups, each section at random, with consent about the use of data.
- Existing classes, not randomized: comparing groups, each section given its condition by you.
- Two AIs: comparing groups, one condition using another agent, such as one with VETTING.
- Units with and without AI: comparing units, one plan.
- Crossover (AB/BA): comparing units, two orders, the second the reverse of the first.
- Waitlist: comparing groups, the later group without AI until a given unit.

## Where it runs

**Where it runs** holds the study's courses and chat pages, up to 40.

- Courses have known learners, each with its own link, class list and sections: one per school, class or online sample.
- A chat page can host an observational study. Each device is an anonymous visitor, shown by visitor code (`V-…`).
- To know who learners are, or to compare, use a course. A comparative study runs on courses only.

A course or chat page is in one study at a time, until that study closes. You can remove one only while nobody has taken part through it.

**How learners sign in** sets one way for every course while the study is open: **Each course's own way**, **Personal codes on cards**, **They type their name or an ID**, or **Their ID comes in the link**. A comparative study needs sign-in that follows each learner, not the device. Sign-in is fixed once the study opens.

## Who changes activities

- **Observational:** the activities stay the course's. Teachers keep changing them, and every record carries its activity version.
- **Comparative:** the first course you add with activities gives the study its design. Its activities move into the study and are changed on **Design**, for every course at once. Other courses must have no activities of their own.

A teacher studying their own course changes its activities in the study too. Teachers still set opening times and extra time. Teachers who run a course join the project as editors.

::: cards
- [Your first study](/docs/research/first-study): start from your situation.
- [Conditions and assignment](/docs/research/conditions): set what differs and who gets which.
:::