> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify-poc.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# corr()

> Calculate the correlation coefficient from a counter aggregate

<Icon icon="tag" iconType="duotone" /> Since [1.3.0][toolkit-1.3.0]

Calculate the correlation coefficient from a counter aggregate. The calculation uses a linear least-squares fit, and
returns a value between 0.0 and 1.0, from no correlation to the strongest possible correlation.

## Samples

Calculate the correlation coefficient to determine the goodness of a linear fit between counter value and time.

```sql theme={"dark"}
SELECT
    id,
    bucket,
    corr(summary)
FROM (
    SELECT
        id,
        time_bucket('15 min'::interval, ts) AS bucket,
        counter_agg(ts, val) AS summary
    FROM foo
    GROUP BY id, time_bucket('15 min'::interval, ts)
) t
```

## Arguments

The syntax is:

```sql theme={"dark"}
corr(
    summary CounterSummary
) RETURNS DOUBLE PRECISION
```

| Name      | Type             | Default | Required | Description                                                    |
| --------- | ---------------- | ------- | -------- | -------------------------------------------------------------- |
| `summary` | `CounterSummary` | -       | ✔        | A counter aggregate created using [`counter_agg`][counter-agg] |

## Returns

| Column | Type             | Description                                                                                                               |
| ------ | ---------------- | ------------------------------------------------------------------------------------------------------------------------- |
| corr   | DOUBLE PRECISION | The correlation coefficient calculated with time as the independent variable and counter value as the dependent variable. |

[counter-agg]: /api-reference/timescaledb-toolkit/counters-and-gauges/counter_agg/counter_agg

[toolkit-1.3.0]: https://github.com/timescale/timescaledb-toolkit/releases/tag/1.3.0