---
title: Introduction
description: "Introduction to the statistical methods Statsig uses to analyze experiments, including hypothesis testing, confidence intervals, and variance reduction."
product: general
last_updated: 2025-09-18
token_estimate: 298
---
# Introduction

> For AI agents: a documentation index is available at [/llms.txt](/llms.txt). Append `.md` to any page URL for markdown, or send `Accept: text/markdown`.

## How the Statsig Stats Engine works

The Statsig Stats Engine powers the experiment results you read in [Pulse](https://docs.statsig.com/experiments/interpreting-results/read-results). It runs a series of calculations to identify the following:

- [Metric deltas](https://docs.statsig.com/experiments/statistical-methods/metric-deltas): The difference in metrics between the test and control groups.
- [Confidence intervals](https://docs.statsig.com/experiments/statistical-methods/confidence-intervals): The gray, red, and green bars in Pulse. They represent the uncertainty in the metric deltas and depend on the [standard error](https://docs.statsig.com/experiments/statistical-methods/variance) of the metrics.
- [p-Values](https://docs.statsig.com/experiments/statistical-methods/p-value): A statistical measurement common in hypothesis testing. Represents the probability of observing a metric delta at least as extreme as the one measured, under the assumption that the treatment has no impact on that metric.