> ## Documentation Index
> Fetch the complete documentation index at: https://runrehearsals.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# What Is a Rehearsal? What Is a Simulation?

> How a Rehearsal and a simulation differ, and how each replica is interviewed by an AI researcher inside one

## Definition

In the product, the study you set up is called a **Rehearsal,** which contains one or more **simulations**. A simulation presents a group of replicas called a **cohort** with a scenario (a price
change, an ad creative, a product choice) inside an environment (real-world context like
macroeconomic conditions, local news, and product research for that replica's area), and collects
their responses.

<Note>
  You create a Rehearsal in the intake chat and launch it from there. See
  [Starting a New Rehearsal](/docs/platform/new-rehearsal) for setup and
  [Running & Monitoring a Rehearsal](/docs/platform/running-a-rehearsal) for what happens after you
  press go.
</Note>

<Note>
  A simulation runs a moderated research interview against a cohort of replicas at once. Each
  replica is interviewed independently, and their individual responses aggregate into a
  distribution rather than a single averaged answer.
</Note>

## The Environment: A Moderated Interview

Every replica in a simulation is interviewed by an AI researcher in a natural, turn-by-turn
conversation. The researcher asks your questions, listens, follows up to draw out genuine
preference and reasoning, and when relevant shows the replica stimuli (images, video, documents)
during the interview, the way a moderator shares a screen in a live study.

<Steps>
  <Step title="The replica enters the scenario" icon="door-open">
    The replica is given any environmental context for the study in its working memory, the
    real-world backdrop the person would be reasoning against. For example, the current economic
    climate, relevant market news, and the product research the person would do before deciding. The scenario itself is then put to them as a question by the researcher, so
    nothing about the person's own situation is assumed.
  </Step>

  <Step title="The researcher conducts the interview" icon="comments">
    An AI researcher asks your questions conversationally, adapting and probing for the real
    reasoning behind an answer instead of accepting a one-word response.
  </Step>

  <Step title="Stimuli are shown when relevant" icon="image">
    If your simulation includes creative or product artifacts, the researcher presents them during
    the conversation and asks the replica to react.
  </Step>

  <Step title="Responses are captured" icon="floppy-disk">
    Each replica's full answers and reasoning are recorded as a transcript.
  </Step>
</Steps>

<Info>
  Responses are open-ended and verbal. Replicas explain their thinking in their own words rather
  than ticking a box. Structured outcomes, like which feature or ad won, are then derived by aggregating
  across all the replicas in the cohort.
</Info>

## Anatomy of a Simulation

| Element   | What it is                                                                                                                                               |
| :-------- | :------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Goal      | The objective of the study, what you are trying to learn                                                                                                 |
| Cohort    | Which population of replicas to interview, built and screened in the [cohort builder](/docs/platform/building-cohorts) (for example, women 22 to 35, \$100K+) |
| Questions | The interview questions, each optionally carrying a private instruction to the researcher                                                                |
| Artifacts | The stimuli shown during the interview: ad creatives, product images, mockups, documents, [uploaded as content](/docs/platform/content-and-data)              |

## How Many Replicas?

By default a simulation interviews about 75 replicas per run. This number is adjustable, and may also fluctuate depending on how specific you make your cohort. Each simulation answers your full question
set independently, so every question is answered by dozens of distinct people. Larger cohorts
can be used to capture more of the variance in divisive or long-tail topics.

## What You Get Out

The immediate output is the set of interview transcripts, with every replica's answers and
reasoning. From there, findings are aggregated into a project report: an executive summary,
recommendations, a participant table describing the cohort, behavioral segments, surprising
findings, and the methodology (sample size, cohort description, number of simulations and
questions, and date range). See [Running & Monitoring a Rehearsal](/docs/platform/running-a-rehearsal)
for how the run progresses and where the report shows up.

<Card title="Next: Simulation Types & Templates" icon="layer-group" href="/docs/methodology/simulation-types" horizontal>
  Pricing, product preference, advertising, and the templates you can start from.
</Card>