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

# Quasi-constant feature count

> Learn how to use the quasi-constant feature count test

## Definition

The quasi-constant feature count test allows you to specify a threshold on the number of features
that are near-constant (low variance).

## Taxonomy

* **Task types**: Tabular classification, tabular regression.
* **Availability**: <Tooltip tip="Continuously evaluate your models and datasets as you iterate on their versions.">development</Tooltip>
  and <Tooltip tip="Monitor a model in production, measure its health, check for drifts and set up alerts.">monitoring</Tooltip>.

## Why it matters

* Quasi-constant features have very low variance and tend to not be as useful for models.
* If a feature shouldn't be quasi-constant but is, you might want to re-normalize it.

## Test configuration examples

If you are writing a `tests.json`, here are a few valid configurations for the character length test:

<CodeGroup>
  ```json Development theme={null}
  [
    {
      "name": "No quasi-constant features",
      "description": "Asserts that there are no quasi-constant features (i.e., with a very low variance)",
      "type": "integrity",
      "subtype": "quasiConstantFeatureCount",
      "thresholds": [
        {
          "insightName": "quasiConstantFeatures",
          "insightParameters": null,
          "measurement": "quasiConstantFeatureCount",
          "operator": "<=",
          "value": 0
        }
      ],
      "subpopulationFilters": null,
      "mode": "development",
      "usesValidationDataset": true, // Apply test to the validation set
      "usesTrainingDataset": false,
      "usesMlModel": false,
      "syncId": "b4dee7dc-4f15-48ca-a282-63e2c04e0689" // Some unique id
    }
  ]
  ```

  ```json Monitoring theme={null}
  [
    {
      "name": "No quasi-constant features",
      "description": "Asserts that there are no quasi-constant features (i.e., with a very low variance)",
      "type": "integrity",
      "subtype": "quasiConstantFeatureCount",
      "thresholds": [
        {
          "insightName": "quasiConstantFeatures",
          "insightParameters": null,
          "measurement": "quasiConstantFeatureCount",
          "operator": "<=",
          "value": 0
        }
      ],
      "subpopulationFilters": null,
      "mode": "monitoring",
      "usesProductionData": true,
      "evaluationWindow": 3600, // 1 hour
      "delayWindow": 0,
      "syncId": "b4dee7dc-4f15-48ca-a282-63e2c04e0689" // Some unique id
    }
  ]
  ```
</CodeGroup>

## Related

* [Quasi-constant features](/tests/integrity/quasi-constant-feature).