# Variant Stats

Pre-calculated stats are useful for filtering variants. This stats are intra-study, calculated within a given cohort.

## Cohorts

Cohorts are defined as a arbitrary group of samples. Cohorts can be defined in Catalog, either selecting samples one by one or selecting all samples that share some attributes like population or phenotype.

If a cohort is modified after calculating the statistics, the existing statistics became **INVALID**.

By default, in each study, there is defined the cohort **ALL** that contains all the samples loaded in the study. Every time that new samples are loaded in the study, this cohort is modified, and the statistics have to be recomputed.

## Stats models

There are two types of statistics, *per variant*, and *global* statistics. Variant statistics are stored in the variants database, within the StudyEntry. Global statistics are stored in Catalog.

**Variant Global Stats **(inter variant)

PENDING

## Aggregated statistics

Usually, public studies do not provide samples data. In this situations is not possible to calculate the statistics. Instead, the statistics can be extracted from the INFO column. Unfortunately, there is no standard way for defining multi-cohort statistics in the VCF format. Instead, OpenCGA recognizes three different formats for representing statistics.

**BASIC **mode**EVS** mode**EXAC** mode