> ## 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 features

> Learn how to use the quasi-constant features test

## Definition

The quasi-constant features test allows you to specify if a certain feature is expected
to be near-constant (low variance) or not.

## Taxonomy

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

## 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:

```json Development theme={null}
[
  {
    "name": "Feature 'Year' is not quasi-constant",
    "description": "Asserts that the feature 'Year' does not have a very low variance",
    "type": "integrity",
    "subtype": "quasiConstantFeature",
    "thresholds": [
      {
        "insightName": "featureProfile",
        "insightParameters": [
            {"name": "name", "value": "Year"}
        ],
        "measurement": "isQuasiConstant",
        "operator": "is",
        "value": false
      }
    ],
    "subpopulationFilters": null,
    "mode": "development",
    "usesValidationDataset": true,
    "usesTrainingDataset": false,
    "usesMlModel": false,
    "syncId": "b4dee7dc-4f15-48ca-a282-63e2c04e0689"
  }
]
```

```json Monitoring theme={null}
[
  {
    "name": "Feature 'Year' is not quasi-constant",
    "description": "Asserts that the feature 'Year' does not have a very low variance",
    "type": "integrity",
    "subtype": "quasiConstantFeature",
    "thresholds": [
      {
        "insightName": "featureProfile",
        "insightParameters": [{ "name": "name", "value": "Year" }],
        "measurement": "isQuasiConstant",
        "operator": "is",
        "value": false
      }
    ],
    "subpopulationFilters": null,
    "mode": "monitoring",
    "usesProductionData": true,
    "evaluationWindow": 3600,
    "delayWindow": 0,
    "syncId": "b4dee7dc-4f15-48ca-a282-63e2c04e0689"
  }
]
```

## Related

* [Quasi-constant feature count](https://docs.openlayer.com/tests/integrity/quasi-constant-feature-count).


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